Optical pickup apparatus, recording/reproducing apparatus provided with the optical pickup apparatus, optical element, and information recording/reproducing method

ABSTRACT

An optical pickup apparatus for reproducing information from an optical information recording medium or for recording information onto an optical information recording medium, is provided with a first light source for emitting first light flux having a first wavelength; a second light source for emitting second light flux having a second wavelength, the first wavelength being different from the second wavelength; a converging optical system having an optical axis and a diffractive portion, and a photo detector; wherein in case that the first light flux passes through the diffractive portion to generate at least one diffracted ray, an amount of n-th ordered diffracted ray of the first light flux is greater than that of any other ordered diffracted ray of the first light flux, and in case that the second light flux passes through the diffractive portion to generate at least one diffracted ray, an amount of n-th ordered diffracted ray of the second light flux is greater than that of any other ordered diffracted ray of the second light flux, where n stands for an integer other than zero.

This is a continuation of application Ser. No. 09/487,928, filed Jan.20, 2000, now U.S. Pat. No. 6,870,805 which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates to an optical pickup apparatus, arecording/reproducing apparatus with the optical pickup apparatus, anoptical element, and an information recording/reproducing method.

Recently, as the practical application of the short wavelength redlaser, a DVD which is a high density optical information recordingmedium (called also optical disk) having almost the same dimension as aCD (compact disk) and the larger capacity, comes into the production. Ina DVD recording/reproducing apparatus, the numerical aperture NA on theoptical disk side of an objective lens when a semiconductor laser of 650nm is used, is 0.6–0.65. The DVD has a track pitch of 0.74 μm, and theminimum pit length of 0.4 μm, and is in densification, in whichdimensions are lower than a half as compared to the CD having the trackpitch of 1.6 μm and the minimum pit length of 0.83 μm. Further, in theDVD, in ordered to suppress the coma which is generated when the opticaldisk is inclined to the optical axis, to be small, the transparentsubstrate thickness is 0.6 mm, which is the half of the transparentsubstrate thickness of the CD.

Further, other than the above-described CD or DVD, various standardoptical disks in which the light source wavelength or the transparentsubstrate thickness is different, for example, CD-R, RW (post scripttype compact disk), VD (video disk), MD (mini-disk), MO(photo-electro-magnetic disk), etc., come in the market and are spread.Further, the wavelength of the semiconductor laser is further shortened,and the short wavelength blue laser having the emission wavelength ofabout 400 nm is being into practical use. When the wavelength isshortened, even if the same numerical aperture as that of the DVD isused, the capacity of the optical information recording medium can befurther increased.

Further, in the same dimension as the CD which is the above-describedconventional optical information recording medium, the development of aplurality of optical information recording media, such as the CD-R inwhich recording and reproducing can be carried out, or the DVD whoserecording density is increased, in which the transparent substratethickness of the recording surface, or the wavelength of the laser lightfor recording and reproducing is different, is advanced, therefore, itis required that the recording and reproducing by the same opticalpickup can be conducted to these optical information recording medium.Accordingly, various optical pickups which have a plurality of laserlight sources corresponding to the using wavelength, and by which thelaser light is converged onto the recording surface by the sameobjective lens by the necessary numerical aperture, are proposed (forexample, Japanese Tokkaihei No. 8-55363, Japanese Tokkaihei No.10-92010, etc.).

In the above description, in Japanese Tokkaihei No. 9-54973, an opticalsystem using a hologram optical element in which 635 nm is used for thetransmitted light (zero ordered diffracted ray) and 785 nm is used for−first ordered diffracted ray, and an optical system using a hologramoptical system in which 635 nm is used for +first ordered diffracted rayand 785 nm is used for the transmitted light (zero ordered diffractedray), are disclosed. Further, in Japanese Tokkaihei No. 10-283668, anoptical system in which, the wavelength is 650 nm, a hologram ring lensis transmitted at 100%, and when 780 nm, the light is first ordereddiffracted by the hologram ring lens, is disclosed.

However, in these hologram element and hologram-shaped ring lens, whendiffraction efficiency of zero ordered light is made to be 100% for thewavelength on one side, there surely is a limitation for diffractionefficiency of +first ordered diffracted ray or of −first ordereddiffracted ray for the wavelength on the other side, and thereby,desirable high diffraction efficiency can not be obtained, a loss of aquantity of light is caused, and efficiency of using a quantity of lightis worsened, which has been a problem. When a loss of a quantity oflight is caused, a laser of higher power is required, especially inrecording of information.

Further, in the hologram element and the hologram-shaped ring lens, whendiffraction efficiency of zero ordered light is made to be 100% for thewavelength on one side, and when diffraction efficiency of +firstordered diffracted ray or of −first ordered diffracted ray is made to begreat by prohibiting zero ordered light from being transmitted as far aspossible, for the wavelength on the other side, the hologram has beenmade to be as deep as 3.8–5.18 μm. Therefore, when a function of ahologram optical element or of a hologram-shaped ring lens is integratedin an objective lens in particular, it is very difficult to process ametal mold and to mold, which has been a problem.

Further, the present inventors previously proposed an objective lens(Japanese Tokuganhei No. 9-286954) which can structure a optical pickupwhich is composed of a plurality of divided surface which are dividedinto concentric circular-like ones, and in which each divided surface isaberration corrected to the diffraction limit to a plurality of lightsources having different wavelength, and/or to the transparent substratehaving the different thickness of the recording surface, and thestructure is simplified. This objective lens has a function by which anecessary aperture can be automatically obtained corresponding to theusing wavelength and/or the thickness of the transparent substrate.However, when a laser/detector integrated unit in which the laser lightsource and light detector are integrated, is used, there is a problemthat a case occurs that the detection can not be correctly conducted dueto a flare light entering into the light detector. This is conspicuousparticularly in the laser/detector integrated unit of a type by whichthe light flux is deflected and introduced into the light detector byusing the hologram. Further, when high speed recording is carried out inrecordable disks in the DVD system (DVD-RAM, DVD-R, DVD-RW, DVD+R, etc.)or recordable disks in the CD system (CD-R, CD-RW, etc.), because apartial light beam becomes flare, the efficiency of use of the lightamount is bad as compared to the optical system using the exclusive uselens, therefore, it is necessary to increase the power of laser lightsource.

To both the DVD and CD whose using wavelength and transparent substratethickness are different from each other, various interchangeable opticalsystems, in which one objective lens is used for recording and/orreproducing the information without generating large sphericalaberration or chromatic aberration, are proposed. However, the opticalsystems which are in practical use, are structured such that thedivergence degree of the divergent light flux from the light source isweakened by a coupling lens, or the divergent light flux is made to theparallel light flux or the weak convergent light flux, and the lightflux is converged onto the information recording surface through theobjective lens and the transparent substrate of the optical informationrecording medium, and accordingly, 2 lenses of the coupling lens and theobjective lens are necessary. Accordingly, it is difficult that the sizeof the optical pickup apparatus is reduced to be small and thin, andthere is a problem that the cost is increased.

On the one hand, as described above, various optical disks except the CDand DVD are spread, and therefore, an optical system which isinterchangeable to these optical disks, and whose structure is simple,and the optical pickup apparatus provided with the optical system arenecessary.

SUMMARY OF THE INVENTION

An object of the invention is to provide a pickup apparatus, a recordingand reproducing apparatus, an optical element and a recording andreproducing method, wherein one pickup apparatus can conduct recordingand/or reproducing of different types of optical information recordingmedia employing rays of light with at least two different wavelengths.

Further object is to make information recording and/or informationreproducing to be conducted by one pickup apparatus, for each differentoptical information recording medium without generating seriousspherical aberration and chromatic aberration even in the case of usingrays of light having at least two different wavelengths and applying todifferent types of optical information recording media. In addition tothat, another object is to provide an optical pickup apparatus having ssimple structure. In particular, when using different types of opticalinformation recording media each having a transparent substrate with adifferent thickness, the problem of spherical aberration becomes moreserious. Further object is that one pickup apparatus can conductrecording and/or reproducing of information for different types ofoptical information recording media without generating serious sphericalaberration and chromatic aberration, even in the aforesaid occasion.

In addition, still further object is that detection of light by an photodetector can be conducted satisfactorily and sigmoid characteristics indetection are made to be satisfactory, without irradiation of flarelight which affects the detection adversely on an photo detector, evenin the case of a pickup apparatus employing an integrated unit composedof plural lasers and plural detectors. Furthermore, providing an opticalpickup apparatus wherein a loss of a quantity of light is less andefficiency of using a quantity of light is excellent, a recording andreproducing apparatus, an optical element and a recording andreproducing method is also an object of the invention.

The above object can be attained by the following structures andmethods.

(1) An optical pickup apparatus for reproducing information from anoptical information recording medium or for recording information ontoan optical information recording medium, comprises:

a first light source for emitting first light flux having a firstwavelength;

a second light source for emitting second light flux having a secondwavelength, the first wavelength being different from the secondwavelength;

a converging optical system having an optical axis and a diffractiveportion, and

a photo detector;

wherein in case that the first light flux passes through the diffractiveportion to generate at least one diffracted ray, an amount of n-thordered diffracted ray of the first light flux is greater than that ofany other ordered diffracted ray of the first light flux, and in casethat the second light flux passes through the diffractive portion togenerate at least one diffracted ray, an amount of n-th ordereddiffracted ray of the second light flux is greater than that of anyother ordered diffracted ray of the second light flux,

where n stands for an integer other than zero.

(2) An optical element for use in an optical pickup apparatus forreproducing information from an optical information recording medium orfor recoding information onto an optical information recording medium,comprises:

an optical axis, and

a diffractive portion,

wherein in case that the first light flux passes through the diffractiveportion to generate at least one diffracted ray, an amount of n-thordered diffracted ray of the first light flux is greater than that ofany other ordered diffracted ray of the first light flux, and in casethat the second light flux whose wavelength is different from that ofthe first light flux passes through the diffractive portion to generateat least one diffracted ray, an amount of n-th ordered diffracted ray ofthe second light flux is greater than that of any other ordereddiffracted ray of the second light flux,

wherein a difference in wavelength between the first light flux and thesecond light flux is 80 nm to 400 nm and n stands for an integer otherthan zero.

(3) An apparatus for reproducing information from an optical informationrecording medium or for recording information onto the opticalinformation recording medium comprises;

-   -   an optical pickup apparatus, comprising a first light source for        emitting first light flux having a first wavelength;        -   a second light source for emitting second light flux having            a second wavelength, the first wavelength being different            from the second wavelength;        -   a converging optical system having an optical axis, a            diffractive portion, and        -   a photo detector,            wherein            in case that the first light flux passes through the            diffractive portion to generate at least one diffracted ray,            an amount of n-th ordered diffracted ray of the first light            flux is greater than that of any other ordered diffracted            ray of the first light flux, and in case that the second            light flux passes through the diffractive portion to            generate at least one diffracted ray, an amount of n-th            ordered diffracted ray of the second light flux is greater            than that of any other ordered diffracted ray of the second            light flux, where n stands for an integer other than zero.            (4) A method of reproducing information from or recording            information on at least two kinds of optical information            recording media by an optical pickup apparatus comprising a            first light source, a second light source, a photo detector            and a converging optical system having an optical axis and a            diffractive portion, the method comprises steps of;

emitting first light flux from the first light source or second lightflux from the second light flux, wherein a wavelength of the secondlight flux is different from a wavelength of the first light flux;

letting the first light or the second light flux pass through thediffractive portion to generate at least one diffracted ray of the firstlight flux or a least one diffracted ray of the second light flux,wherein when an amount of n-th ordered diffracted ray among the at leastone diffracted ray of the first light flux is greater than an amount ofany other ordered diffracted ray of the first light flux, an amount ofn-th ordered diffracted ray among the at least one diffracted ray of thesecond light flux is greater than an amount of any other ordereddiffracted ray of the second light flux,

converging, by the converging optical system, the n-th ordereddiffracted ray of the first light flux onto a first informationrecording plane of a first optical information recording medium or then-th ordered diffracted ray of the second light flux onto a secondinformation recording plane of a second optical information recordingmedium in order for the optical pickup apparatus to record theinformation onto or reproduce the information from the first informationrecording plane or the second information recording plane,

detecting, by a photo detector, a first reflected light flux of theconverged n-th ordered diffracted light from the first informationrecording plane or a second reflected light flux of the converged n-thordered diffracted light from the second information recording plane;

where n stands for an integer other than zero.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of the optical path of a diffraction optical lens ofExample 1 of the present invention.

FIG. 2 is a view of the spherical aberration to a wavelength λ=635 nm bythe diffraction optical lens of Example 1 of the present invention.

FIG. 3 is a view of the spherical aberration up to NA 0.45 to awavelength λ=780 nm by the diffraction optical lens of Example 1 of thepresent invention.

FIG. 4 is a view of the spherical aberration up to NA 0.60 to thewavelength λ=780 nm by the diffraction optical lens of Example 1 of thepresent invention.

FIG. 5 is a view of the wave front aberration to the wavelength λ=635 nmby the diffraction optical lens of Example 1 of the present invention.

FIG. 6 is a view of the wave front aberration to the wavelength λ=780 nmby the diffraction optical lens of Example 1 of the present invention.

FIG. 7 is a view of the optical path to the wavelength λ=405 nm by adiffraction optical lens of Example 2 of the present invention.

FIG. 8 is a view of the optical path to the wavelength λ=635 nm by thediffraction optical lens of Example 2 of the present invention.

FIG. 9 is a view of the spherical aberration to the wavelength λ=405 nmby the diffraction optical lens of Example 2 of the present invention.

FIG. 10 is a view of the spherical aberration to the wavelength λ=635 nmby the diffraction optical lens of Example 2 of the present invention.

FIG. 11 is a view of the wave front aberration to the wavelength λ=405nm by the diffraction optical lens of Example 2 of the presentinvention.

FIG. 12 is a view of the wave front aberration to the wavelength λ=635nm by the diffraction optical lens of Example 2 of the presentinvention.

FIG. 13 is a view of the optical path to the wavelength λ=405 nm by adiffraction optical lens of Example 3 of the present invention.

FIG. 14 is a view of the optical path to the wavelength λ=635 nm by thediffraction optical lens of Example 3 of the present invention.

FIG. 15 is a view of the spherical aberration to the wavelength λ=405 nmby the diffraction optical lens of Example 3 of the present invention.

FIG. 16 is a view of the spherical aberration to the wavelength λ=635 nmby the diffraction optical lens of Example 3 of the present invention.

FIG. 17 is a view of the wave front aberration to the wavelength λ=405nm by the diffraction optical lens of Example 3 of the presentinvention.

FIG. 18 is a view of the wave front aberration to the wavelength λ=635nm by the diffraction optical lens of Example 3 of the presentinvention.

FIG. 19 is a view of the optical path by a diffraction optical lens ofExample 4 of the present invention.

FIG. 20 is a view of the spherical aberrations to the wavelengths λ=635nm, 650 nm, and 780 nm by the diffraction optical lens of Example 4 ofthe present invention.

FIG. 21 is a view of the optical path by a diffraction optical lens ofExample 5 of the present invention.

FIG. 22 is a view of the spherical aberrations to the wavelengths λ=635nm, 650 nm, and 780 nm by the diffraction optical lens of Example 5 ofthe present invention.

FIG. 23 is a view of the optical path to the wavelength λ=650 nm, by adiffraction optical lens of Example 6 of the present invention.

FIG. 24 is a view of the optical path to the wavelength λ=780 nm(NA=0.5), by the diffraction optical lens of Example 6 of the presentinvention.

FIG. 25 is a view of the spherical aberration up to the numeral aperture0.60 to the wavelength λ=650±10 nm, by the diffraction optical lens ofExample 6 of the present invention.

FIG. 26 is a view of the spherical aberration up to the numeral aperture0.50 to the wavelength λ=780±10 nm, by the diffraction optical lens ofExample 6 of the present invention.

FIG. 27 is a view of the spherical aberration up to the numeral aperture0.60 to the wavelength λ=780 nm, by the diffraction optical lens ofExample 6 of the present invention.

FIG. 28 is a view of the wave front aberration rms to the wavelengthλ=650 nm, by the diffraction optical lens of Example 6 of the presentinvention.

FIG. 29 is a view of the wave front aberration rms to the wavelengthλ=780 nm, by the diffraction optical lens of Example 6 of the presentinvention.

FIG. 30 is a view of the optical path to the wavelength λ=650 nm, by adiffraction optical lens of Example 7 of the present invention.

FIG. 31 is a view of the optical path to the wavelength λ=780 nm(NA=0.5), by the diffraction optical lens of Example 7 of the presentinvention.

FIG. 32 is a view of the spherical aberration up to the numeral aperture0.60 to the wavelength λ=650±10 nm, by the diffraction optical lens ofExample 7 of the present invention.

FIG. 33 is a view of the spherical aberration up to the numeral aperture0.50 to the wavelength λ=780±10 nm, by the diffraction optical lens ofExample 7 of the present invention.

FIG. 34 is a view of the spherical aberration up to the numeral aperture0.60 to the wavelength λ=780 nm, by the diffraction optical lens ofExample 7 of the present invention.

FIG. 35 is a view of the wave front aberration rms to the wavelengthλ=650 nm, by the diffraction optical lens of Example 7 of the presentinvention.

FIG. 36 is a view of the wave front aberration rms to the wavelengthλ=780 nm, by the diffraction optical lens of Example 7 of the presentinvention.

FIG. 37 is a view of the optical path to the wavelength λ=650 nm, by adiffraction optical lens of Example 8 of the present invention.

FIG. 38 is a view of the optical path to the wavelength λ=780 nm(NA=0.5), by the diffraction optical lens of Example 8 of the presentinvention.

FIG. 39 is a view of the spherical aberration up to the numeral aperture0.60 to the wavelength λ=650±10 nm, by the diffraction optical lens ofExample 8 of the present invention.

FIG. 40 is a view of the spherical aberration up to the numeral aperture0.50 to the wavelength λ=780±10 nm, by the diffraction optical lens ofExample 8 of the present invention.

FIG. 41 is a view of the spherical aberration up to the numeral aperture0.60 to the wavelength λ=780 nm, by the diffraction optical lens ofExample 8 of the present invention.

FIG. 42 is a view of the wave front aberration rms to the wavelengthλ=650 nm, by the diffraction optical lens of Example 8 of the presentinvention.

FIG. 43 is a view of the wave front aberration rms to the wavelengthλ=780 nm, by the diffraction optical lens of Example 8 of the presentinvention.

FIG. 44 is a graph showing the relationship of the number of thediffraction annular bands and the height from the optical axis of thediffraction optical lens of the Example 6 of the present invention.

FIG. 45 is a graph showing the relationship of the number of thediffraction annular bands and the height from the optical axis of thediffraction optical lens of the Example 7 of the present invention.

FIG. 46 is a graph showing the relationship of the number of thediffraction annular bands and the height from the optical axis of thediffraction optical lens of the Example 8 of the present invention.

FIG. 47 is a view typically showing the relationship of the diffractionlens power and the lens shape of the diffraction optical lens accordingto Examples of the present invention.

FIG. 48 is a view of the optical path showing the structure of theoptical pickup apparatus according to the second embodiment of thepresent invention.

FIG. 49 is a view of the optical path showing the structure of theoptical pickup apparatus according to the third embodiment of thepresent invention.

FIG. 50 is a view of the optical path to the wavelength λ=650 nm of theobjective lens in Example 9 of the present invention.

FIG. 51 is a view of the optical path to the wavelength λ=780 nm of theobjective lens in Example 9 of the present invention.

FIG. 52 is a view of the spherical aberration to the wavelength λ=650 nmof the objective lens of Example 9 of the present invention.

FIG. 53 is a view of the spherical aberration up to NA 0.45 to thewavelength λ=780 nm of the objective lens of Example 9 of the presentinvention.

FIG. 54 is a view of the spherical aberration up to 0.60 to thewavelength λ=780 nm of the objective lens of Example 9 of the presentinvention.

FIG. 55 is a view of the wave front aberration to the wavelength λ=650nm of the objective lens of Example 9 of the present invention.

FIG. 56 is a view of the wave front aberration to the wavelength λ=780nm of the objective lens of Example 9 of the present invention.

FIG. 57 is a view of the optical path to the wavelength λ=650 nm of theobjective lens of Example 10 of the present invention.

FIG. 58 is a view of the optical path to the wavelength λ=400 nm of theobjective lens of Example 10 of the present invention.

FIG. 59 is a view of the optical path to the wavelength λ=780 nm of theobjective lens of Example 10 of the present invention.

FIG. 60 is a view of the spherical aberration to the wavelength λ=650 nmof the objective lens of Example 10 of the present invention.

FIG. 61 is a view of the spherical aberration to the wavelength λ=400 nmof the objective lens of Example 10 of the present invention.

FIG. 62 is a view of the spherical aberration up to NA 0.45 to thewavelength λ=780 nm of the objective lens of Example 10 of the presentinvention.

FIG. 63 is a view of the spherical aberration up to NA 0.65 to thewavelength λ=780 nm of the objective lens of Example 10 of the presentinvention.

FIG. 64 is a view of the wave front aberration to the wavelength λ=650nm of the objective lens of Example 10 of the present invention.

FIG. 65 is a view of the wave front aberration to the wavelength λ=400nm of the objective lens of Example 10 of the present invention.

FIG. 66 is a view of the wave front aberration to the wavelength λ=780nm of the objective lens of Example 10 of the present invention.

FIG. 67 is a view showing the structure of the optical pickup apparatusaccording to Embodiment 4 of the present invention.

FIG. 68 is a view of the optical path to the wavelength λ=650 nm of theobjective lens of Example 11 of the present invention.

FIG. 69 is a view of the optical path to the wavelength λ=400 nm of theobjective lens of Example 11 of the present invention.

FIG. 70 is a view of the optical path to the wavelength λ=780 nm of theobjective lens of Example 11 of the present invention.

FIG. 71 is a view of the spherical aberration to the wavelength λ=650 nmof the objective lens of Example 11 of the present invention.

FIG. 72 is a view of the spherical aberration to the wavelength λ=400 nmof the objective lens of Example 11 of the present invention.

FIG. 73 is a view of the spherical aberration up to the numericalaperture 0.45 to the wavelength λ=780 nm of the objective lens ofExample 11 of the present invention.

FIG. 74 is a view of the spherical aberration up to the numericalaperture 0.65 to the wavelength λ=780 nm of the objective lens ofExample 11 of the present invention.

FIG. 75 is a view of the wave front aberration to the wavelength λ=650nm of the objective lens of Example 11 of the present invention.

FIG. 76 is a view of the wave front aberration to the wavelength λ=400nm of the objective lens of Example 11 of the present invention.

FIG. 77 is a view of the wave front aberration to the wavelength λ=780nm of the objective lens of Example 11 of the present invention.

FIG. 78 is a view of the optical path to the wavelength λ=650 nm of theobjective lens of Example 12 of the present invention.

FIG. 79 is a view of the optical path to the wavelength λ=400 nm of theobjective lens of Example 12 of the present invention.

FIG. 80 is a view of the optical path to the wavelength λ=780 nm of theobjective lens of Example 12 of the present invention.

FIG. 81 is a view of the spherical aberration to the wavelength λ=650 nmof the objective lens of Example 12 of the present invention.

FIG. 82 is a view of the spherical aberration to the wavelength λ=400 nmof the objective lens of Example 12 of the present invention.

FIG. 83 is a view of the spherical aberration up to the numericalaperture 0.45 to the wavelength λ=780 nm of the objective lens ofExample 12 of the present invention.

FIG. 84 is a view of the spherical aberration up to the numericalaperture 0.65 to the wavelength λ=780 nm of the objective lens ofExample 12 of the present invention.

FIG. 85 is a view of the wave front aberration to the wavelength λ=650nm of the objective lens of Example 12 of the present invention.

FIG. 86 is a view of the wave front aberration to the wavelength λ=400nm of the objective lens of Example 12 of the present invention.

FIG. 87 is a view of the wave front aberration to the wavelength λ=780nm of the objective lens of Example 12 of the present invention.

FIG. 88 is a view of the optical path to the wavelength λ=650 nm of theobjective lens of Example 13 of the present invention.

FIG. 89 is a view of the optical path to the wavelength λ=400 nm of theobjective lens of Example 13 of the present invention.

FIG. 90 is a view of the optical path to the wavelength λ=780 nm of theobjective lens of Example 13 of the present invention.

FIG. 91 is a view of the spherical aberration to the wavelength λ=650 nmof the objective lens of Example 13 of the present invention.

FIG. 92 is a view of the spherical aberration to the wavelength λ=400 nmof the objective lens of Example 13 of the present invention.

FIG. 93 is a view of the spherical aberration up to the numericalaperture 0.45 to the wavelength λ=780 nm of the objective lens ofExample 13 of the present invention.

FIG. 94 is a view of the spherical aberration up to the numericalaperture 0.65 to the wavelength λ=780 nm of the objective lens ofExample 13 of the present invention.

FIG. 95 is a view of the wave front aberration to the wavelength λ=650nm of the objective lens of Example 13 of the present invention.

FIG. 96 is a view of the wave front aberration to the wavelength λ=400nm of the objective lens of Example 13 of the present invention.

FIG. 97 is a view of the wave front aberration to the wavelength λ=780nm of the objective lens of Example 13 of the present invention.

FIG. 98 is a view of the optical path to the wavelength λ=400 nm, of theobjective lens of Example 13 of the present invention.

FIG. 99 is a view of the spherical aberration to the wavelength λ=400nm±10 nm, of the objective lens of Example 13 of the present invention.

FIG. 100 is a view of the spherical aberration to the wavelength λ=650nm±10 nm, of the objective lens of Example 13 of the present invention.

FIG. 101 is a view of the spherical aberration to the wavelength λ=780nm±10 nm, of the objective lens of Example 13 of the present invention.

FIG. 102 is a view of the optical path showing the first structure ofthe optical pickup apparatus according to Embodiment 8 of the presentinvention.

FIG. 103 is a view of the optical path showing the second structure ofthe optical pickup apparatus according to Embodiment 8 of the presentinvention.

FIG. 104 is a view of the optical path showing the third structure ofthe optical pickup apparatus according to Embodiment 8 of the presentinvention.

FIG. 105 is a view of the optical path showing the fourth structure ofthe optical pickup apparatus according to Embodiment 8 of the presentinvention.

FIG. 106 is a view of the optical path showing the fifth structure ofthe optical pickup apparatus according to Embodiment 8 of the presentinvention.

FIG. 107 is a view of the optical path showing the sixth structure ofthe optical pickup apparatus according to Embodiment 8 of the presentinvention.

FIG. 108 is a view of the optical path showing the seventh structure ofthe optical pickup apparatus according to Embodiment 8 of the presentinvention.

FIG. 109 is a typical view showing the structure of the optical disk ofSuper RENS system.

FIG. 110 is a graph showing the relationship of the image formationmagnification m2 and the wave front aberration of the objective lens ofthe Example 15 according to Embodiment 8 of the present invention.

FIG. 111 is a sectional view of Example 15 according to Embodiment 8 ofthe present invention.

FIG. 112 is a view of the spherical aberration of Example 15.

FIG. 113 is an illustration of an action of the diffraction pattern.

FIG. 114 is a typical view showing an influence of the chromaticaberration on the spherical aberration of the objective lens accordingto Embodiment 8 of the present invention.

FIG. 115 is a typical view showing an influence of +first ordereddiffraction on the spherical aberration of the objective lens accordingto Embodiment 8 of the present invention.

FIG. 116 is a typical view showing an influence of −first ordereddiffraction on the spherical aberration of the objective lens accordingto Embodiment 8 of the present invention.

FIG. 117 is a view of the optical path showing the structure of theoptical pickup apparatus according to Embodiment 7 of the presentinvention.

FIG. 118 is a view of the optical path of the diffraction optical lens(the objective lens having the diffraction surface) which is theobjective lens of Example 15 according to Embodiment 7 of the presentinvention.

FIG. 119 is a view of the spherical aberration up to the numericalaperture 0.60 to the wavelengths (λ)=640, 650, 660 nm of the diffractionoptical lens in FIG. 118.

FIG. 120 is a view of the optical path of the diffraction optical lensin the case where the thickness of the transparent substrate of theoptical information medium is larger than that in FIG. 118, in Example15.

FIG. 121 is a view of the spherical aberration up to the numericalaperture 0.60 to the wavelength λ=770, 780, 790 nm of the diffractionoptical lens in FIG. 120.

FIG. 122 is a view of the optical path of the diffraction optical lens(the objective lens having the diffraction surface) which is theobjective lens in Example 16 according to Embodiment 7 of the presentinvention.

FIG. 123 is a view of the spherical aberration up to the numericalaperture 0.60 to the wavelength (λ)=640, 650, 660 nm of the diffractionoptical lens in FIG. 122.

FIG. 124 is a view of the optical path of the diffraction optical lensin the case where the thickness of the transparent substrate of theoptical information medium is larger than that in FIG. 122, in Example16.

FIG. 125 is a view of the spherical aberration up to the numericalaperture 0.60 to the wavelength (λ)=770, 780, 790 nm of the diffractionoptical lens in FIG. 124.

FIG. 126 is a view of the optical path of the diffraction optical lens(the objective lens having the diffraction surface) which is theobjective lens in Example 17 according to Embodiment 7 of the presentinvention.

FIG. 127 is a view of the spherical aberration up to the numericalaperture 0.60 to the wavelength (λ)=640, 650, 660 nm of the diffractionoptical lens in FIG. 126.

FIG. 128 is a view of the optical path of the diffraction optical lensin the case where the thickness of the transparent substrate of theoptical information medium is larger than that in FIG. 126, in Example17.

FIG. 129 is a view of the spherical aberration up to the numericalaperture 0.60 to the wavelength (λ)=770, 780, 790 nm of the diffractionoptical lens in FIG. 128.

FIG. 130 is a view of the optical path of the diffraction optical lens(the objective lens having the diffraction surface) which is theobjective lens in Example 18 according to Embodiment 7 of the presentinvention.

FIG. 131 is a view of the spherical aberration up to the numericalaperture 0.70 to the wavelength (λ)=390, 400, 410 nm of the diffractionoptical lens in FIG. 130.

FIG. 132 is a view of the optical path of the diffraction optical lensin the case where the thickness of the transparent substrate of theoptical information medium is larger than that in FIG. 130, in Example18.

FIG. 133 is a view of the spherical aberration up to the numericalaperture 0.70 to the wavelength λ=640, 650, 660 nm of the diffractionoptical lens in FIG. 132.

FIG. 134 is an illustration showing a cross sectional view of adiffractive annular band.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An optical pickup apparatus for reproducing information from an opticalinformation recording medium or for recording information onto anoptical information recording medium has therein a first light sourcefor emitting first light flux having a first wavelength, a second lightsource for emitting second light flux having a second wavelength, thefirst wavelength being different from the second wavelength, aconverging optical system having an optical axis, a diffractive portion,and a photo detector. Further, the diffractive portion generates moren-th ordered diffracted ray than other ordered diffracted ray in thefirst light flux which has passed the diffractive portion, and generatesmore n-th ordered diffracted ray than other ordered diffracted ray alsoin the second light flux which has passed the diffractive portion. nstands for an integer other than zero. The optical element of theinvention is one having a diffraction portion which makes the aforesaidembodiment possible. An apparatus for reproducing information from anoptical information recording medium or for recording information ontothe optical information recording medium has the optical pickupapparatus stated above.

(11-1)

Incidentally, “an amount of n-th ordered diffracted ray being greaterthan that of any other ordered diffracted ray 11” means that thediffraction efficiency for the n-th ordered diffracted ray is higherthan that for the other ordered diffracted ray other than the n-thordered diffracted ray. Further, n in n-th ordered includes also a sign,and when +first ordered diffracted ray is generated more than otherordered diffracted ray in the first light flux which has passed thediffractive portion, it is intended that +first ordered diffracted rayis generated more than other ordered diffracted ray even in the secondlight flux which has passed the diffractive portion, and it does notinclude that −first ordered diffracted ray is generated more than otherordered diffracted ray in the second light flux which has passed thediffractive portion.

(11-2)

The optical pickup apparatus of the invention is one wherein one pickupapparatus can conduct recording and/or reproducing optical informationrecording media in different types employing at least two wavelengthseach being different from others. Namely, the optical pickup apparatusof the invention is one used for recording/reproducing of differentinformation recording media such as a first optical informationrecording medium and a second optical information recording medium. Afirst light source of the optical pickup apparatus emits first lightflux for reproducing information from a first optical informationrecording medium or for recording information onto the first opticalinformation recording medium, while, a second light source of theoptical pickup apparatus emits second light flux for reproducinginformation from a second optical information recording medium or forrecording information onto the second optical information recordingmedium. Usually, an optical information recording medium has atransparent substrate on an information recording plane.

(11-3)

When putting the function of the invention in another way, theconverging optical system is capable of converging “n-th ordereddiffracted ray of the first light flux”, which is generated at thediffractive portion by the first light flux being reached thediffractive portion, on a first information recording plane of the firstoptical information recording medium through a first transparentsubstrate, to reproduce information recorded in the first opticalinformation recording medium or to record information onto the firstoptical information recording medium, and the converging optical systemis capable of converging “n-th ordered diffracted ray in the secondlight flux”, which is generated at the diffractive portion by the secondlight flux being reached the diffractive portion, on a secondinformation recording plane of the second optical information recordingmedium through a second transparent substrate, to reproduce informationrecorded in the second optical information recording medium or to recordinformation onto the second optical information recording medium, andthe photo detector is capable of receiving light flux reflected from thefirst information recording plane or the second information recordingplane.

(11-4)

There will be shown as follows the embodiment which is more preferable,wherein the converging optical system is capable of converging n-thordered diffracted ray in the first light flux on a first informationrecording plane of the first optical information recording medium underthe state that wave-front aberration is not larger than 0.07 λrms withinthe prescribed numerical aperture of the first optical informationrecording medium in the first light flux on the image side of theobjective lens (in other words, under the state wherein the light fluxwithin the prescribed numerical aperture takes diffraction limitcapacity or less in the best image point (best focus)), and theconverging optical system is capable of converging n-th ordereddiffracted ray in the second light flux on a second informationrecording plane of the second optical information recording medium underthe state that wave-front aberration is not larger than 0.07 λrms withinthe prescribed numerical aperture of the second optical informationrecording medium in the second light flux on the image side of theobjective lens (in other words, under the state wherein the light fluxwithin the prescribed numerical aperture takes diffraction limitcapacity or less in the best image point (best focus)).

Further, it is preferable that n-th ordered diffracted ray is convergedunder the state that wave-front aberration is not larger than 0.07 λrmswithin the prescribed numerical aperture on the image side of theobjective lens on each information recording plane, even in the case ofwavelength shift of about ±10 nm or less caused by temperaturefluctuation and electric current fluctuation, in the first light sourceor in the second light source. In particular, it is especiallypreferable that n-th ordered diffracted ray is converged under the stateof 0.07 λrms or less within the prescribed numerical aperture on theimage side of the objective lens, even when the first light flux or thesecond light flux is one having a wavelength of 600 nm or less (forexample, 350 nm–480 nm) and wavelength shifting of about ±10 nm or lessis generated.

(11-5)

Incidentally, when n-th ordered diffracted ray is +first ordereddiffracted ray or −first ordered diffracted ray, a loss of a quantity oflight is less than that in an occasion where a diffracted ray of higherordered than ±first ordered is used, which is preferable.

Further, when a diffraction efficiency of n-th ordered diffracted ray ofthe first light flux in the diffractive portion is represented by A% anda diffraction efficiency of diffracted ray of other certain-th ordered(preferably, the number of ordered with the greatest diffractionefficiency among number of ordered other than n) is represented by B %,it is preferable to satisfy A–B≧10, while, when a diffraction efficiencyof n-th ordered diffracted ray of the second light flux in thediffractive portion is represented by A′% and a diffraction efficiencyof diffracted ray of other certain-th ordered is represented by B′%, itis preferable to satisfy A′–B′≧10. The condition of A–B≧30 and A′–B′≧30is more preferable, that of A–B≧50 and A′–B′≧50 is still morepreferable, and that of A–B≧70 and A′–B′≧70 is further more preferable.

(11-6)

When both of the first light flux and second light flux are used forrecording of information on optical information recording medium, it ispreferable that diffraction efficiency of n-th ordered diffracted ray inthe diffractive portion is made to be maximum at the wavelength betweenthe wavelength of the first light flux and the wavelength of the secondlight flux.

(11-7)

When either of the first light flux and second light flux alone is usedfor recording of information on optical information recording medium andthe other light flux is used for reproduction only, it is preferablethat diffraction efficiency of n-th ordered diffracted ray in thediffractive portion is made to be minimum at the wavelength between thewavelength of the first light flux and the wavelength of the secondlight flux. The more preferable is that the diffraction efficiency ofthe n-th ordered diffracted ray in the diffractive portion is made to bemaximum at one of the wavelength of the first light flux and thewavelength of the second light flux in using for recording ofinformation.

(11-8)

As an optical element on which the diffractive portion is provided, alens having a refraction surface and a flat type element both providedon the converging optical system are given, though there is nolimitation in particular.

When a lens having a refraction surface as an optical element on which adiffractive portion is provided, there are given an objective lens, acollimator lens and a coupling lens as a concrete example of the opticalelement. On the refraction surfaces on each of these lenses, adiffractive portion can be provided. A flat-shaped or lens-shapedoptical element which is intended only to be provided with a diffractiveportion may also be added to a converging optical system.

Incidentally, when providing a diffraction portion on a refractionsurface of an objective lens, it is preferable that an outside diameterof the objective lens (outside diameter including a flange if the flangeis provided) is larger than an aperture diameter by 0.4 mm–2 mm.

(11-9)

The diffractive portion may be provided either on an optical surface ofthe optical element on the light source side, or on the image side(optical information recording medium side), or on both sides. Further,the diffractive portion may be provided either on the convex surface oron the concave surface.

(11-10)

When a diffractive portion is provided on an objective lens, it is morepreferable because the number of parts is reduced and errors in assemblyof an optical pickup apparatus in manufacturing can be reduced. In thatcase, it is preferable that the objective lens is of a single-elementtype, but it may also be of a two-element type. A plastic lens ispreferable, but a glass lens is also acceptable. It is also possible toprovide on the surface of a glass lens a resin layer on which adiffractive portion is formed. It is preferable that the objective lenson which the diffractive portion is provided has on its outercircumference a flange section having a surface extending in thedirection perpendicular to an optical axis. This makes it easy to mounton the pickup apparatus accurately, and makes it possible to obtainstable performance even when ambient temperature fluctuates. It isfurther preferable that the refraction surface of the objective lens isan aspheric surface and a diffractive portion is provided on theaspheric surface. The diffractive portion may naturally be providedeither on one side of the objective lens or on both sides thereof.

(11-11)

Further, it is preferable that an optical element on which a diffractiveportion is provided is made of a material with Abbe's number νd of notless than 50 and not more than 100. It may either be made of plastic orbe made of glass. Incidentally, in the case of a plastic lens, it ispreferable that a refractive index of its material is in a range of1.4–1.75, and the range of 1.48–1.6 is more preferable and that of1.5–1.56 is further preferable.

When the diffractive portion is provided on a lens (preferably on aplastic lens), it is preferable that the following conditionalexpression is satisfied, for obtaining an optical pickup apparatus andan optical element which are stable against temperature fluctuation.−0.0002/° C.<Δn/ΔT<−0.00005° C.wherein,

ΔT: Temperature fluctuation

Δn: Amount of change of refractive index of the lens

It is further preferable to satisfy the following conditionalexpression.0.05 nm/° C.<Δλ1/ΔT<0.5 nm/° C.wherein,

-   -   Δλ1 (nm): Amount of change of wavelength of first light source        for temperature fluctuation ΔT        (11-12)

The diffractive portion is preferably a phase type one from theviewpoint of efficiency of using light, though it may also be anamplitude type one. It is preferable that the diffractive pattern of thediffractive portion is shaped to be symmetry rotatable in relation tothe optical axis. It is preferable that the diffractive portion hasplural annular bands when viewed in the direction of the optical axis,and these plural annular bands are formed mostly on the concentriccircle whose center is on the optical axis or in the vicinity of theoptical axis. A circle is preferable, but it may also be an ellipse. Ablaze type ring-zonal diffraction surface having steps is especiallypreferable. It may further be a ring-zonal diffraction surface which isformed stepwise. It may further be a ring-zonal diffraction surfacewhich is formed stepwise as annular bands which shift discretely in thedirection where lens thickness is greater as its position becomes moredistant from the optical axis. Incidentally, it is preferable that thediffractive portion is ring-zonal, but it may also be a 1-dimensionaldiffraction grating.

(11-13)

When the diffraction portion represents concentric circles in aring-zonal form, a pitch of diffraction annular bands is defined by theuse of a phase difference function or an optical path differencefunction. In this case, it is preferable that a coefficient other thanzero is owned by at least one term other than a squared term in a phasedifference function expressed by a power series which shows positions ofplural annular bands. Due to this structure, it is possible to correctspherical aberration of chromatic aberration caused by rays of lighteach having a different wavelength.

(11-14)

When a coefficient other than zero is owned by a squared term in a phasedifference function expressed by a power series which shows positions ofplural annular bands of the diffractive portion, paraxial chromaticaberration can be corrected, which is preferable. However, when it isimportant not to make a pitch of diffraction annular bands to be toosmall, it is also possible to make the phase difference functionexpressed by a power series which shows positions of plural annularbands of the diffractive portion to include no squared term.

(11-15)

Incidentally, it is preferable that the number of steps of diffractionannular bands of the diffractive portion is in a range from 2 to 45. Themore preferable is not more than 40. Still further preferable is notmore than 15. Incidentally, counting of the number of steps is achievedby counting the number of stepped sections of annular bands.

Further, it is preferable that a depth of the stepped section ofdiffraction annular bands of the diffraction portion in the direction ofthe optical axis is not more than 2 μm. Due to this structure, anoptical element can be manufactured easily, and n-th ordered diffractedray can easily be made to be +first ordered diffracted ray or −firstordered diffracted ray.

Further, when providing a diffraction portion on the surface of anoptical element on the light source side, it is preferable that a depthof a stepped section becomes greater as the stepped section becomes moredistant from an optical axis.

(11-16)

With regard to the effect of the diffractive portion to deflect thelight flux, in the present specification, the case that the light fluxis deflected toward the optical axis is called as the positive effect,on the other hand, the case that the light flux is deflected so as to beshifted away from the optical axis is called as the negative effect.

With regard to the pitch on the ring-zonal diffraction surface, theremay also be provided a pitch wherein a pitch is provided to be inverselyproportional to a height from an optical axis. It is also possible toprovide a pitch having aspheric characteristics wherein the way ofproviding a pitch is not inversely proportional to a height from anoptical axis.

In particular, when providing a pitch having aspheric characteristics,namely, when a pitch is not provided to be inversely proportional to aheight from an optical axis, it is preferable that there is no point ofinflection in the function of optical path difference, though there mayalso be the point of inflection.

Further, the diffraction effect added in the diffractive portion mayeither be positive on the entire surface of the diffractive portion, orbe negative on the entire surface of the diffractive portion. It is alsopossible to arrange so that a plus or minus sign of the diffractioneffect added in the diffractive portion is switched at least one time inthe direction to become more distant from the optical axis in thedirection perpendicular to the optical axis. For example, there is givena type wherein a sign is changed from minus to plus in the direction tobecome more distant from the optical axis in the direction perpendicularto the optical axis, as shown in FIG. 47( c). In other words, it can besaid that plural annular bands of the diffractive portion are blazed,and on the diffractive annular band closer to the optical axis, itsstepped section is positioned to be away from the optical axis, and onthe diffractive annular band farther from the optical axis, its steppedsection is positioned to be closer to the optical axis. There can alsobe given a type wherein a sign is changed from plus to minus in thedirection to become more distant from the optical axis in the directionperpendicular to the optical axis, as shown in FIG. 47( d). In otherwords again, it can be said that plural annular bands of the diffractiveportion are blazed, and on the aforesaid diffractive annular band closerto the optical axis, its stepped section is positioned to be closer tothe optical axis, and on the diffractive annular band farther from theoptical axis, its stepped section is positioned to be farther from theoptical axis.

Incidentally, the pitch (zone distance) of diffraction annular bandsmeans distance p in FIG. 134 between a step of a annular band and a stepof its adjacent annular band in the direction perpendicular to theoptical axis, while, a depth of the step means length d in FIG. 134 ofthe step in the optical direction.

(11-17)

Incidentally, when the pitch is smaller, converging effect and divergingeffect on that portion become stronger, and when pitch is greater,converging effect and diverging effect on that portion become weaker

Further, the diffractive portion may also be provided on the entireportion of the surface through which a light flux passes, in an opticalelement having a diffractive portion. In other words, it can be saidthat it is also possible to arrange so that the all light flux withinthe maximum numerical aperture at an image side of an objective lens maypass through the diffractive portion. A diffractive portion may also beprovided simply on the entire portion on one optical surface of anoptical element, or not less than 70% (not less than 80% is preferableand not less than 90% is more preferable) of one optical surface of theoptical element may be made to be a diffractive portion.

(11-18)

Further, the diffractive portion may also be provided on only a part ofthe surface of an optical element through which a light flux passes, tomake another area to be a refraction surface or a transmission surface,in an optical element. When a diffractive portion is provided only on apart of the surface through which a light flux passes, the diffractiveportion may be provided only on a portion in the vicinity of an opticalaxis including the optical axis, or the diffractive portion may beprovided to be in a ring shape, without being provided to be in thevicinity of the optical axis. For example, a diffractive portion may beprovided on 10% or more and less than 90% of one surface in opticalsurfaces of an optical element. Or, 10% or more and less than 50% of onesurface may be made to be a diffractive portion.

(11-19)

Incidentally, when providing a diffractive portion only on a part of thesurface of an optical element through which a light flux passes,NA1>NAH1, NAH1≧NA2, NA2≧NAL1≧0 is preferable in the case of NA1>NA2. Inthe case of NA2>NA1, NA2>NAH2, NAH2≧NA1, NA1≧NAL2≧0 is preferable.Incidentally, each of NA1 and NA2 is a prescribed numerical aperture ofan objective lens on the image side, when using the first light flux andthe second light flux respectively. Each of NAH1 and NAH2 is a numericalaperture of the objective lens on the image side for each of the firstlight flux and the second light flux passing through the outermost sideof the diffractive portion. Each of NAL1 and NAL2 is a numericalaperture of the objective lens on the image side for each of the firstlight flux and the second light flux passing through the innermost sideof the diffractive portion.

(11-20)

When the diffractive portion is provided only on a part of the surfaceof an optical element through which a light flux passes, it ispreferable that the light flux which has passed the diffraction portionat NA1 or less in the first light flux and light which has passed therefraction surface at NA1 or less other than the diffractive portion areconverged at mostly the same position, in the case of NA1>NA2. In thecase of NA2>NA1, it is preferable that the light flux which has passedthe diffraction portion at NA2 or less in the second light flux andlight which has passed the refraction surface at NA2 or less other thanthe diffractive portion are converged at mostly the same position.

An embodiment wherein the diffractive portion has the first diffractionpattern and the second diffraction pattern, and the second diffractionpattern is farther than the first diffraction pattern in terms of adistance from the optical axis. It is possible to combine a diffractiveportion and a refraction surface having no diffractive portion on thesame plane.

(11-21)

When two types of diffraction patterns are used, it is also possible toarrange so that n-th ordered diffracted ray is generated more than otherordered diffracted ray in the first light flux which has passed thefirst diffraction pattern of the diffractive portion and is capable tobe converged on a first information recording plane, and n-th ordereddiffracted ray is generated more than other ordered diffracted ray alsoin the second light flux which has passed the first diffraction patternof the diffractive portion and is capable to be converged on a secondinformation recording plane, and n-th ordered diffracted ray isgenerated more than other ordered diffracted ray in the first light fluxwhich has passed the second diffraction pattern of the diffractiveportion and is capable to be converged on a first information recordingplane, while, 0-th ordered light representing transmitted light isgenerated more than other ordered diffracted ray in the second lightflux which has passed the second diffraction pattern of the diffractiveportion. The n-th ordered in this case is preferably first ordered.

(11-22)

Further, in another embodiment, n-th ordered diffracted ray is generatedmore than other ordered diffracted ray in the first light flux which haspassed the first diffraction pattern of the diffractive portion and iscapable to be converged on a first information recording plane, and n-thordered diffracted ray is generated more than other ordered diffractedray also in the second light flux which has passed the first diffractionpattern of the diffractive portion and is capable to be converged on asecond information recording plane, and 0-th ordered diffracted ray isgenerated more than other ordered diffracted ray in the first light fluxwhich has passed the second diffraction pattern of the diffractiveportion and is capable to be converged on a first information recordingplane, while, diffracted ray not of n-th ordered but of negative orderedis generated more than other ordered diffracted ray in the second lightflux which has passed the second diffraction pattern of the diffractiveportion. The n-th ordered in this case is preferably +first ordered, andnegative ordered is preferably −first ordered.

(11-23)

In the case of an optical pickup apparatus or an optical element used inplural optical information recording media each having a differentthickness of a transparent substrate, it is especially preferable that apitch of annular bands of the diffraction portion satisfies thefollowing conditional expression.0.4<=|(Ph/Pf)−2|<=25

The more preferable is 0.8≦|(Ph/Pf)−2|≦6, and further preferable is1.2≦|(Ph/Pf)−2|≦2

(11-24)

A pitch of annular bands of the diffractive portion corresponding to themaximum numerical aperture of the objective lens on the image side isrepresented by Pf, and a pitch of annular bands of the diffractiveportion corresponding to ½ of the maximum numerical aperture isrepresented by Ph. Incidentally, with regard to the maximum numericalaperture, the greatest one among prescribed numerical apertures of sometypes of optical information recording media subjected to informationreading/recording in an optical pickup apparatus is regarded as themaximum numerical aperture. Incidentally, the prescribed numericalaperture means a numerical aperture which makes reading/recording ofinformation on optical information recording medium by a light fluxwhich has a prescribed wavelength possible in its optical pickupapparatus, but it may also be a numerical aperture stipulated by thestandard of a certain optical information recording medium. Further, “apitch of annular bands of the diffractive portion corresponding to themaximum numerical aperture of the objective lens on the image side”means a pitch of annular bands located at the outermost portion of thelight flux passing through the diffraction portion in the case of themaximum numerical aperture. “A pitch of annular bands of the diffractiveportion corresponding to ½ of the maximum numerical aperture” means apitch of annular bands located at the outermost portion of the lightflux passing through the diffraction portion in the case of thenumerical aperture which is a half of the maximum numerical aperture.

(11-25)

Incidentally, there will be accepted an optical pickup apparatus whereinup to the prescribed numerical aperture is made to be no-aberration forone light flux among two light fluxes respectively from two lightsources, and for the portion outside the prescribed numerical aperture,aberration is made to be flare.

(11026)

In other words, it can be said as follows. The first light flux which iswithin a prescribed numerical aperture, of a first optical informationrecording medium, of the objective lens on the image side in the case ofusing a first light flux is converged on a first information recordingplane of the first optical information recording medium under the stateof 0.07 λrms or less, and the first light flux passing through theoutside of the prescribed numerical aperture of the objective lens onthe image side in the case of using a first light flux is made to begreater than 0.07 λrms on a first information recording plane, and thesecond light flux passing through the prescribed numerical aperture ofthe objective lens on the image side in the case of using a first lightflux as well as the second light flux passing through the outside of theaforesaid numerical aperture are converged on a second informationrecording plane under the state of 0.07 λrms or less. In this case, NA1is smaller than NA2, and a light flux between NA1 and NA2 is made to beflare when recording and reproducing the first optical informationrecording medium.

(11-27)

Or, the second light flux which is within a prescribed numericalaperture, of a second optical information recording medium, of theobjective lens on the image side in the case of using a second lightflux is converged on a second information recording plane of the secondoptical information recording medium under the state of 0.07 λrms orless, and the second light flux passing through the outside of aprescribed numerical aperture of the objective lens on the image side inthe case of using a second light flux is made to be greater than 0.07λrms on a second information recording plane, and the first light fluxpassing through the prescribed numerical aperture of the objective lenson the image side in the case of using a second light flux as well asthe first light flux passing through the outside of the aforesaidnumerical aperture are converged on a first information recording planeunder the state of 0.07 λrms or less. In this case, NA1 is greater thanNA2, and a light flux between NA2 and NA1 is made to be flare, whenrecording and reproducing the second optical information recordingmedium.

These embodiments can be established voluntarily by the design of adiffraction portion. For example, it is possible either to provide adiffractive portion on the entire surface of an optical element andthereby to generate flare at the prescribed numerical aperture or moreby designing the diffractive portion, or to provide a diffractiveportion on a part of the surface of an optical element and to make theother part to be a refraction surface so that flare may be generated bythe refraction surface and the diffractive portion.

(11-28)

In the embodiment to generate flare stated above, it is preferable thatan aperture regulating means to block or diffract the first light fluxoutside a prescribed numerical aperture of the objective lens on theimage side in the case of using the first light flux and to transmit thesecond light flux and an aperture regulating means to block or diffractthe second light flux outside a prescribed numerical aperture of theobjective lens on the image side in the case of using the second lightflux and to transmit the first light flux are not provided. Namely, itis preferable to provide an ordinary aperture only without providing adichroic filter or a hologram filter. If the diffractive portion is onlydesigned to satisfy the aforesaid function, it is enough to provide onlyan ordinary aperture, which is preferable because a mechanism is simple.

(11-29)

However, it is also possible to use a filter such as a hologram filterto generate flare. Incidentally, when providing a filter such as ahologram filter, a separated filter may be provided in the opticalconverging system, or a filter may be provided on the objective lens.

It is possible either to provide flare to be under for the position tomake the minimum spot when the light flux located where the prescribednumerical aperture is more smaller are converged, or to provide flare tobe over. The preferable is to provide to be over.

When generating flare as stated above, it is possible to generate flarecontinuously on the spherical aberration diagram or to generate flarediscontinuously.

Further, an another embodiment, there is given an embodiment of anoptical pickup apparatus wherein no flare is generated. The followingone is given.

(11-30)

In other words, it is possible to express as follows. The first lightflux which is within a prescribed numerical aperture, of a first opticalinformation recoding medium, of the objective lens on the image side inthe case of using the first light flux is converged on a firstinformation recording plane of a first optical information recordingmedium under the state of 0.07 λrms or less, and the first light fluxwhich has passed the outside of a prescribed numerical aperture of theobjective lens on the image side in the case of using the first lightflux is converged on the first information recording plane under thestate of 0.07 λrms or less, or it is blocked and does not reach thefirst information recording plane. The second light flux which haspassed the inside of a prescribed numerical aperture of the objectivelens on the image side in the case of using the first light flux, andthe second light flux which has passed the outside of a prescribednumerical aperture are converged on a second information recording planeof a second optical information recording medium under the state of 0.07λrms or less. In this case, NA1 is smaller than NA2, and a light fluxbetween NA1 and NA2 is also converged or blocked, when conductingrecording or reproducing for the first optical information recordingmedium.

(11-31)

Or, the second light flux which is within a prescribed numericalaperture, of a second optical information recoding medium, of theobjective lens on the image side in the case of using the second lightflux is converged on a second information recording plane of a secondoptical information recording medium under the state of 0.07 λrms orless, and the second light flux which has passed the outside of aprescribed numerical aperture of the objective lens on the image side inthe case of using the second light flux is converged on the secondinformation recording plane under the state of 0.07 λrms or less, or itis blocked and does not reach the second information recording plane.The first light flux which has passed the inside of a prescribednumerical aperture of the objective lens on the image side in the caseof using the second light flux, and the first light flux which haspassed the outside of a prescribed numerical aperture are converged on afirst information recording plane of a first optical informationrecording medium under the state of 0.07 λrms or less. In this case, NA1is greater than NA2, and a light flux between NA2 and NA1 is alsoconverged or blocked, when conducting recording or reproducing for thesecond optical information recording medium.

These embodiments can be established voluntarily by the design of thediffractive portion.

(11-32)

In the embodiment wherein the flare is not generated and a light fluxbetween NA1 and NA2 or between NA2 and NA1 is blocked, it is preferableto provide an aperture regulating means which blocks the first lightflux which is outside a prescribed numerical aperture of the objectivelens on the image side in the case of using the first light flux andtransmits the second light flux, or an aperture regulating means whichblocks the second light flux which is outside a prescribed numericalaperture of the objective lens on the image side in the case of usingthe second light flux and transmits the first light flux. Or, it ispreferable to provide an aperture regulating means wherein each lightflux has its own prescribed numerical aperture.

(11-33)

Namely, it is preferable that a light flux is blocked by a ring-zonalfilter such as a dichroic filter or a hologram filter representing anaperture regulating means at the prescribed numerical aperture or morefor either one of the first light flux or the second light flux.Incidentally, when providing a dichroic filter or a hologram filter, aseparate filter may be provided in an optical converging system, or afilter may be provided on an objective lens.

(11-34)

However, even when no flare is generated, it is also possible to makeall light fluxes within the maximum numerical aperture to be convergedon an information recording plane by providing only an ordinary aperturewithout providing a dichroic filter or a hologram filter. In otherwords, it is also possible to make the first light flux and the secondlight flux within the maximum numerical aperture of the objective lenson the image side to be converged on an information recording planeunder the state of 0.07 λrms. It may be preferable that no flare isgenerated by the above embodiment when NA1=NA2.

(11-35)

Incidentally, the first optical information recording medium and thesecond optical information recording medium both representing differentinformation recording media mean information recording media each havinga different wavelength of light used for each recording/reproducing. Athickness and a refractive index of a transparent substrate may eitherbe the same or be different. A prescribed numerical aperture may eitherbe the same or be different. A prescribed numerical aperture may eitherbe the same or be different, and the recording density for informationalso may be the same or be different.

Paraxial chromatic aberration and spherical aberration caused by adifference of a wavelength of light used for recording/reproducing ofeach of different information recording media are corrected by thediffractive portion of the invention. Incidentally, it is mostpreferable that both spherical aberration and paraxial chromaticaberration are corrected, and an embodiment wherein spherical aberrationonly is corrected and paraxial chromatic aberration is not corrected ispreferable next, while, an embodiment wherein paraxial chromaticaberration only is corrected and spherical aberration is not correctedis also acceptable. Incidentally, as a concrete embodiment of theoptical information recording medium, CD, CD-R, CD-RW, DVD, DVD-RAM, LD,MD, MO and so on may be listed. However, it may be not limited to these.Further, an optical information recording medium employing blue lasermay be used.

(11-36)

Even in the case where a thickness of a transparent substrate isdifferent in different information recording media, and sphericalaberration is caused based on the thickness of the transparentsubstrate, the spherical aberration is corrected by the diffractiveportion of the invention. Incidentally, when a thickness of atransparent substrate is different in a first optical informationrecording medium and a second optical information recording medium, alevel of the caused spherical aberration is higher, and therefore, theeffect of the invention is more remarkable, which is preferable.

(11-37)

Incidentally, it is preferable that a difference between the wavelengthof the first light flux and the wavelength of the second light flux isin a range from 80 nm to 400 nm. The more preferable is in a range from100 nm to 200 nm. Further preferable is in a range from 120 nm to 200nm. As the first light source and the second light source, it ispossible to select two types of light sources from those emitting lightof wavelengths 760–820 nm, 630–670 nm and 350–480 nm, for example, tocombine them for use. Three light sources or four light sources arenaturally acceptable. When the third light source emitting the thirdlight flux and the fourth light source emitting the fourth light fluxare provided, it is preferable that n-th ordered diffracted ray isgenerated more than other ordered diffracted ray even in the third lightflux and the fourth light flux which have passed the diffractiveportion.

(11-38)

When the wavelength of the second light flux is longer than thewavelength of the first light flux, it is preferable that paraxialchromatic aberration in the second light flux and that in the firstlight flux satisfy the following conditional expression.−λ₂/(2NA ₂ ²)≦Z≦λ ₂/(2NA ₂ ²)

λ₂: Wavelength of the second light flux

NA₂: Prescribed numerical aperture, of the second optical informationrecording medium, of the objective lens on the image side for the secondlight flux

(11-39)

When a recording medium having a different thickness of a transparentsubstrate is used, it is preferable that the following expression issatisfied in the case of t2>t1 and λ2>λ1.0.2×10⁻⁶/° C.<ΔWSA3·λ1/{f·(NA1)⁴ ·ΔT}<2.2×10⁻⁶/° C.

NA1: Prescribed numerical aperture, of the first optical informationrecording medium, of the objective lens on the image side for the use ofthe first light flux

λ1: Wavelength of the first light flux

f1: Focal length of the objective lens for the first light flux

ΔT: Ambient temperature fluctuation

ΔWSA3 (λ1 rms): An amount of fluctuation of 3-ordered sphericalaberration component of spherical aberration of a light flux convergedon an optical information recording plane in the case of reproducing orrecording the optical information recording medium by the use of thefirst light flux

(11-40)

It is also possible to arrange so that the first light flux representinga non-collimated light flux such as diverged light or converged light ismade to enter the objective lens in the case of using the first lightflux, and the second light flux representing a non-collimated light fluxsuch as diverged light or converged light is made to enter the objectivelens in the case of using the second light flux.

(11-41)

Or, the first light flux representing a collimated light flux may bemade to enter the objective lens in the case of using the first lightflux, and the second light flux representing a non-collimated light fluxsuch as diverged light or converged light may also be made to enter theobjective lens in the case of using the second light flux. Or, it isalso possible to arrange so that the first light flux representing anon-collimated light flux such as diverged light or converged light ismade to enter the objective lens in the case of using the first lightflux, and the second light flux representing a collimated light is madeto enter the objective lens in the case of using the second light flux.

When using a non-collimated light flux in either of the first light fluxand the second light flux, or in both light fluxes of them, it ispreferable that an absolute value of a difference between magnificationm1 of an objective lens in using the first light flux and magnificationm2 of an objective lens in using the second light flux is in a range of0– 1/15. The more preferable range is 0– 1/18. In the case of λ2>λ1 andt2>t1, it is preferable that m1 is greater. In particular, when usingthe second light flux and the first light flux respectively for CD andDVD, the aforesaid range is preferable. Incidentally, a wavelength ofthe first light source is represented by λ1, a wavelength of the secondlight source is represented by λ2, a thickness of the first transparentsubstrate is represented by t1 and a thickness of the second transparentsubstrate is represented by t2.

Or, it is also possible to arrange so that the first light fluxrepresenting a collimated light flux and the second light fluxrepresenting a collimated light flux may also be made to enter theobjective lens. In this case, it is preferable that the diffractiveportion is in the form shown in FIGS. 47( a) and 47(b), although it mayalso be in the form shown in FIGS. 47( b) and 47(c).

(11-42)

Further, it is also possible to provide, on an optical pickup apparatus,a divergence changing means which changes divergence of a light fluxentering an objective lens, and thereby to change divergence of a lightflux entering an objective lens in the first light flux and the secondlight flux.

Incidentally, when a diverged light enters an objective lens, it ispreferable that the objective lens is a glass lens.

Incidentally, when reproducing and recording can be conducted only foreither one of the first information recording medium and the secondinformation recording medium, and reproducing only is conducted for theother one of them, it is preferable that an image forming magnificationof the total optical pickup apparatus for the first light flux isdifferent from an image forming magnification of the total opticalpickup apparatus for the second light flux, in the optical pickupapparatus. In this case, an image forming magnification of the objectivelens for the first light flux may either be equal to or be differentfrom an image forming magnification of the objective lens for the secondlight flux.

Further, when reproducing and recording can be conducted only for thefirst information recording medium, and reproducing only is conductedfor the second information recording medium in the case of λ1<λ2 andt1<t2, it is preferable that the image forming magnification of thetotal optical pickup apparatus for the first light flux is smaller thanthat of the total optical pickup apparatus for the second light flux.Further, when the foregoing is satisfied in the case of 0.61<NA1<0.66,it is preferable that a coupling lens which changes a magnification isprovided between the first light source and a collimator lens in theoptical converging system, and a collimator lens for the first lightflux and a collimator lens for the second light flux are providedseparately in the optical converging system. Incidentally, it ispreferable that both of the image forming magnification of the objectivelens for the first light flux and the image forming magnification of theobjective lens for the second light flux are zero. Incidentally, awavelength of the first light source is represented by λ1, a wavelengthof the second light source is represented by λ2, a thickness of thefirst transparent substrate is represented by t1, a thickness of thesecond transparent substrate is represented by t2, and a prescribednumerical aperture of the objective lens which is necessary forrecording or reproducing of the first optical information recordingmedium on the image side is represented by NA1.

Further, when reproducing and recording can be conducted only for thesecond information recording medium, and reproducing only is conductedfor the first information recording medium in the case of λ1<λ2 andt1<t2, it is preferable that the image forming magnification of thetotal optical pickup apparatus for the first light flux is greater thanthat of the total optical pickup apparatus for the second light flux.Incidentally, it is preferable that both of the image formingmagnification of the objective lens for the first light flux and theimage forming magnification of the objective lens for the second lightflux are zero.

Incidentally, when reproducing and recording can be conducted for boththe first information recording medium and the second informationrecording medium, or when reproducing only is conducted for both ofthem, it is preferable that an image forming magnification of the totaloptical pickup apparatus for the first light flux is the almost samewith an image forming magnification of the total optical pickupapparatus for the second light flux, in the optical pickup apparatus. Inthis case, an image forming magnification of the objective lens for thefirst light flux may either be equal to or be different from an imageforming magnification of the objective lens for the second light flux.

(11-43)

Further, the photo detector may be made to be common for both the firstlight flux and the second light flux. Or, it is also possible to providea second photo detector so that the photo detector is made to be for thefirst light flux, and the second photo detector is made to be for thesecond light flux.

(11-44)

The photo detector and the first light source or the photo detector andthe second light flux may be unitized. Or, the photo detector, the firstlight source and the second light source may be unitized. Or, the photodetector, the second photo detector, the first light source and thesecond light source may all be unitized integrally. Further, the firstlight source and second light source only may be unitized.

In particular, when the first light source and the second light sourceare unitized respectively and are arranged side by side on the sameplane, it is preferable to provide the first light source on the opticalaxis of the objective lens in the case of NA1>NA2, and it is preferableto provide the second light source on the optical axis of the objectivelens in the case of NA1<NA2. Incidentally, a prescribed numericalaperture of the objective lens which is necessary for recording orreproducing of the first optical information recording medium on theimage side is represented by NA1, and a prescribed numerical aperture ofthe objective lens which is necessary for recording or reproducing ofthe second optical information recording medium on the image side isrepresented by NA2.

Incidentally, when WD1 represents a working distance in recording andreproducing the first optical information recording medium and WD2represents a working distance in recording and reproducing the secondoptical information recording medium, |WD1–WD2|≦0.29 mm is preferable.In this case, it is preferable that a magnification for recording andreproducing of the first optical information recording medium is thesame as that for recording and reproducing of the second opticalinformation recording medium. The more preferable is that themagnification is zero. Further, in the case of t1<t2 and λ1<λ2, WD1≧WD2is preferable. These conditions about a working distance are especiallypreferable when the first optical information recording medium is DVDAND the second optical information recording medium is CD. Incidentally,when the aforesaid working distance is satisfied, the form of thediffractive portion shown in FIGS. 47( b) and 47(c) is more preferablethan that shown in FIGS. 47( a) and 47(d).

Further, the converging optical system or the optical element such as anobjective lens forms a spot so that a light flux may be converged on aninformation recording plane of an optical information recording mediumfor recording and reproducing of information. In particular, when NA1 isgreater than NA2 and λ1 is smaller than λ2, and a light flux outside NA2is made to be flare (wave-front aberration on an image forming plane ismade to be greater than 0.07 λ2rms) on the second information recordingplane of the second optical information recording medium, concerning thesecond light flux, it is preferable that the spot satisfies thefollowing conditions.0.66λ2/NA2≦w≦1.15λ2/NA2w>0.83λ2/NA1

λ1: Wavelength of first light flux

λ2: Wavelength of second light flux

NA1: Prescribed numerical aperture of a first optical informationrecording medium for first light flux

NA2: Prescribed numerical aperture of a second optical informationrecording medium for second light flux

w: Beam diameter of 13.5% intensity of second light flux on imageforming plane

Incidentally, when the spot is not a complete round, it is preferablethat the beam diameter in the direction where the beam diameter isconverged most is made to be the aforesaid beam diameter (w).

It is more preferable that the following conditions are satisfied.0.74λ2/NA2≦w≦0.98λ2/NA2

With regard to a form of the spot, it may either be one wherein a spotof high light intensity used for recording and reproducing is located atthe center, and flare which is low in terms of light intensity to thedegree not to affect the detection adversely is located continuouslyaround the spot, or be one wherein a spot of high light intensity usedfor recording and reproducing is located at the center, and flare islocated around the spot in the form of a doughnut.

(11-45)

Further, in order to detect information very well, it may be preferablethat S-shaped characteristic is good. More concretely, it may bepreferable that over shoot is 0% to 20%.

When λ1 represents a wavelength of the first light source, λ2 representsa wavelength of the second light source, t1 represents a thickness ofthe first transparent substrate, t2 represents a thickness of the secondtransparent substrate, NA1 represents a prescribed numerical aperture ofan objective lens on the image side which is needed for recording orreproducing the first optical information recording medium by firstlight flux, and NA2 represents a prescribed numerical aperture of anobjective lens on the image side which is needed for recording orreproducing the second optical information recording medium by secondlight flux, there is given the following conditional expression as apreferable example. In this case, it is preferable that n-th ordereddiffracted ray is positive first ordered diffracted ray. A preferableembodiment is not naturally limited to the following conditionalexpression.λ1<λ2t1<t2NA1>NA2(preferably,NA1>NA2>0.5×NA1)

In the case that the above conditional formula is satisfied, theobjective lens of the converging optical system comprises a diffractiveportion, and in the case that the converging optical system convergesthe n-th ordered diffracted ray in the second light flux having passedover the diffractive portion on the second information recording planeof the second information recording medium, the spherical aberration maycomprises a discontinuing section in at least one place as shown in FIG.112.

In case of comprising the discontinuing section, at a place near NA2, itmay be preferable that the spherical aberration may comprises adiscontinuing section. For example, following case may be listed. At aplace where NA=0.45, the spherical aberration comprises a discontinuingsection, and at a place where NA=0.5, the spherical aberration comprisesa discontinuing section.

In case that the spherical aberration comprises a discontinuing section,the converging optical system converges the n-th ordered diffracted rayhaving a numerical aperture smaller than NA1 in the first light fluxhaving passed over the diffractive portion on the first informationrecording plane of the first recording medium such that the wave-frontaberration at the best image point is 0.07 λrms and the convergingoptical system converges the n-th ordered diffracted ray having anumerical aperture smaller than that of the discontinuing section in thesecond light flux having passed over the diffractive portion on thesecond information recording plane of the second recording medium suchthat the wave-front aberration at the best image point is 0.07 λrms.

Further, in the case that the above conditional formula is satisfied, itmay be that the conversion optical system comprises an objective lens,and the objective lens has a diffractive portion, in case that theconverging optical system converges the n-th ordered diffracted ray ofthe second light flux having passed over the diffractive portion on thesecond information recording plane of the second optical informationrecording medium in order to conduct the recording or the reproducingfor the second optical information recording medium, the sphericalaberration is continued without having a discontinuing section as shownin FIG. 27.

In the case that the spherical aberration is continued without having adiscontinuing section, it may be preferable that the sphericalaberration at NA1 is not smaller than 20 μm and the spherical aberrationat NA2 is not larger than 10 μm. It may be more preferable tht thespherical aberration at NA1 is not smaller than 50 μm and the sphericalaberration at NA2 is not larger than 2 μm.

(11-46)

There is given the following embodiment as a concrete and preferableexample wherein one type of DVD is used as a first optical informationrecording medium and one type of CD is used as a second opticalinformation recording medium in the aforesaid condition, to which theinvention is not limited.

0.55 mm<t1<0.65 mm

1.1 mm<t2<1.3 mm

630 nm<λ1<670 nm

760 nm<λ2<820 nm

0.55<NA1<0.68

0.40<NA2<0.55

When the diffractive portion is ring-zonal diffraction in the case ofthe aforesaid range, it is preferable that the diffraction portioncorresponding to NA2 or less is not more than 19 annular bands or notless than 21 annular bands. It is also preferable that the totaldiffraction portion is not less than 35 annular bands or not more than33 annular bands.

(11-47)

Further, in the case that the above range is satisfied, it may bepreferable that the diameter of spot satisfy the following embodiment.The conversion optical system comprises an objective lens, the objectivelens has a diffractive portion, λ1=650 nm, t1=0.6 mm, and NA1=0.6, andwherein in case that the first light flux which is composed of parallelrays and have a uniform intensity distribution are introduced in theobjective lens and are converged on the first information recordingplane through the first transparent substrate, a diameter of convergedspot is 0.88 μm to 0.91 μm at the best focusing condition.

Further, it may be preferable that λ1=650 nm, t1=0.6 mm, and NA1=0.65and wherein in case that the first light flux which is composed ofparallel rays and have a uniform intensity distribution are introducedin the objective lens and are converged on the first informationrecording plane through the first transparent substrate, a diameter ofconverged spot is 0.81 μm to 0.84 μm at the best focusing condition.

Furthermore, in the case that the above range is satisfied and thediffractive portion is provided on an objective lens, a pitch of thediffractive portion at NA=0.4 is 10 μm to 70 μm. It may be morepreferable that the pitch is 20 μm to 50 μm.

Further, there is given the following embodiment as a concrete andpreferable example in the aforesaid condition, but the invention is notlimited to this. When conducting also recording for CD as a secondoptical information recording medium, in particular, it is preferablethat NA2 is 0.5. Further, when conducting recording also for the firstoptical information recording medium as DVD, NA1 which is 0.65 ispreferable.

t1=0.6 mm

t2=1.2 mm

λ1=650 nm

λ2=780 nm

NA1=0.6

NA2=0.45

(11-48)

The following embodiment is also acceptable. In the case of thefollowing embodiment, it is preferable that n-th ordered diffracted rayis negative first ordered light.

λ1<λ2

-   -   t1>t2        (11-49)

As a concrete example of an optical information recording mediumreproducing or recording apparatus for reproducing information from anoptical information recording medium or for recording information ontothe optical information recording medium, having an optical pickupapparatus of the invention, there are given a DVD/CD reproducingapparatus, a DVD/CD/CD-R recording and reproducing apparatus, aDVD-RAM/DVD/CD-R/CD recording and reproducing apparatus, a DVD/CD/CD-RWrecording and reproducing apparatus, a DVD/LD reproducing apparatus,DVD/an optical information recording medium recording and reproducingapparatus employing blue laser, CD/and an optical information recordingmedium recording and reproducing apparatus employing blue laser, towhich the invention is not limited. These optical information recordingmedium reproducing or recording apparatuses have a power supply and aspindle motor in addition to the optical pickup apparatus.

Next, a preferable embodiment of the present invention will beexplained.

In ordered to attain the above object, an optical system of Item 1includes more than 1 optical element, and in the optical system used forat least either one of recording or reproducing of the information ontoor from an information recording medium, at least one of the opticalelements has a diffraction surface which selectively generates the sameordered diffracted ray for the light of at least 2 wavelengths which aredifferent from each other.

According to Item 1, because the optical element has the diffractionsurface, the spherical aberration can be corrected for the light of atleast 2 wavelengths which are different from each other, and the axialchromatic aberration can also be corrected. That is, by a simplestructure in which many optical elements such as the objective lens, orsimilar lenses, are used in common with each other, the sphericalaberration and the axial chromatic aberration can be corrected, thereby,the size and weight of the optical system can be reduced, and the costcan be reduced. Further, because the optical system has a diffractionsurface which selectively generates the same ordered diffracted ray forthe light of at least 2 wavelengths which are different from each other,the loss of the light amount can be reduced, and even when the necessarynumerical apertures are different, for example, by using the commonobjective lens, a sufficient light amount can be obtained.

Further, in the optical system of Item 2, in an optical system in whichmore than 1 optical element is included and which is used for at leastone of recording and reproducing of the information onto or from theinformation recording medium, the diffraction surface which selectivelygenerates respectively a specific ordered of the diffracted ray for thelight having at lest 2 wavelengths which are different from each otheris formed on almost entire surface of at least one optical surface of atleast one optical element of the above-described optical elements.

According to Item 2, because the diffraction surface is formed on theoptical element, in the same manner as Item 1, the spherical aberrationand the axial chromatic aberration can be corrected for the light havingat lest 2 wavelengths which are different from each other. Further,because the diffraction surface is formed on almost entire surface of atleast one optical surface of the optical element, the correction can bemore effectively carried out.

Incidentally, each term is defined as follows. Initially, an opticalelement indicates each of all optical elements applicable to the opticalsystem to record the information onto the information recording mediumand/or to reproduce the information on the information recording medium,and generally, a coupling lens, objective lens, polarizing beamsplitter, ¼ wavelength plate, or beam splitter to synthesize the lightfrom more than 2 light sources, or the like, are listed, however, theoptical element is not limited to these. Further, the optical elementwhich is provided with only the diffractive portion of the presentinvention and has not the other function, may be used.

Further, an optical system in the present invention is more than 1assemblage of the optical elements to enable recording of theinformation onto or reproducing of the information on, for example, theCD and DVD, and may mean not only the whole optical system to enablerecording of the information onto the information recording mediumand/or reproducing of the information on the information recordingmedium, but also may means a portion of the optical system, and anoptical system includes at least 1 optical element as described above.

As the information recording medium in the present invention, thedisk-like information recording media, for example, each kind of CD suchas the CD, CD-R, CD-RW, CD-Video, CD-ROM, etc., or each kind of DVD suchas the DVD, DVD-ROM, DVD-RAM, DVD-R, DVD-RW, etc., or the MD, LD, MO orthe like, are listed. Generally, a transparent substrate exists on theinformation recording surface of the information recording medium.Needless to say, the information recording media is not limited theabove. The information recording media used in the present inventioncomprises an optical information recording media such as a blue laseravailable in a current market.

In the present invention, recording of the information onto theinformation recording medium, or reproducing of the information on theinformation recording medium mean to record the information onto theinformation recording surface of the information recording medium, andto reproducing the information recorded on the information recordingsurface. The pickup apparatus and the optical system in the presentinvention may a pickup apparatus and be an optical system used for onlyrecording, or only reproducing, and may also be a pickup apparatus andan optical system used for both of recording and reproducing. Further,the pickup apparatus and the optical system may be used for recordingonto one information recording medium and for reproducing from anotherinformation recording medium, or for recording and reproducing for oneinformation recording medium, and for recording and reproducing foranother information recording medium. Incidentally, the reproducing usedherein includes only reading-out of the information.

Further, the pickup apparatus and the optical system used for at leasteither one of recording or reproducing for the information recordingmedium includes a pickup apparatus and an optical system, of course,applicable for the above purpose, and also a pickup apparatus and anoptical system which is actually used, or intended to be used for suchthe purpose.

In the present invention, the light having at least 2 wavelengths whichare different from each other, may be the light having 2 differentwavelengths, for example, the light having 780 nm wavelength used forthe CD, and 635 nm or 650 nm wavelength used for the DVD, and may be thelight having 3 different wavelengths, which further includes, forexample, the light having 400 nm wavelength for recording and/orreproducing of the large capacity information recording medium which isdensification-recorded. Of course, the light having more than 4different wavelengths may be allowable. Further, even in the opticalsystem in which, actually, more than 3 different wavelengths are used,or the optical system in which that is intended, of course, it means thelight having at least 2 different wavelengths in them. As a matter ofcourse, a combination of 400 nm and 780 nm or a combination of 400 nmand 650 nm may be used.

In the present invention, the light having different wavelength meansthe light having a plurality of wavelengths with a sufficient differenceof wavelength from each other, which is used corresponding to kinds ofthe information recording medium, as described above, or the differenceof the recording density, however, it does not means the light havingthe wavelength which differs due to the temporary shift within about ±10nm caused by the temperature change or output change of 1 light sourcewhich outputs the light having 1 wavelength. Further, as factors thatthe light having different wavelengths is used, other than theabove-described kinds of the information recording media or thedifference of recording density, for example, the difference of thethickness of the transparent substrate of the information recordingmedium, or the difference between recording and reproducing, is listed.

Further, the diffraction surface means the surface in which a relief isprovided on the surface of the optical element, for example, on thesurface of the lens, and which has the function to converge or divergethe flux of light by the diffraction, and when there is an area in whichthe diffraction occurs, and an area in which the diffraction does notoccur on the same optical surface, it means the area in which thediffraction occurs. As the shape of the relief, for example, aconcentric ring band is formed around the optical axis on the surface ofthe optical element, and when the cross section is viewed on the planeincluding the optical axis, it is known that each ring band,(hereinafter, the ring band is called the annular band), has the sawtooth-like shape, and the diffraction surface includes such the shape.

Generally, from the diffraction surface, the infinite ordered diffractedray, such as zero ordered light, ±first ordered light, ±second orderedlight, . . . , is generated, and in the case of the diffraction surfacein which the meridian cross section has the saw-toothed relief asdescribed above, the shape of the relief can be set so that thediffraction efficiency of the specific ordered is made higher than thatof the other ordered, or in a certain circumstance, the diffractionefficiency of a specific one ordered (for example, +first ordered light)is made almost 100%. In the present invention, the diffracted ray of thespecific ordered is selectively generated, means that, to the lighthaving a predetermined wavelength, the diffraction efficiency of thediffracted ray of the specific ordered is higher than that of respectivediffracted ray of the other ordered except the specific ordered, and tothe respective light having 2 wavelength which are different from eachother, the specific ordered of the specific ordered diffracted ray whichis respectively selectively generated, is the same ordered, means thatthe same ordered diffracted ray is selectively generated. Herein, theordered of the diffracted ray is the same, means that the ordered of thediffracted ray is the same including its sign.

Further, the diffraction efficiency is obtained such that the rate ofthe light amount of the diffracted ray of respective ordereds to the alldiffracted ray is obtained according to the shape of the diffractionsurface (the shape of the relief), and obtained by a calculation by thesimulation in which the wavelength of the light to be irradiated is setto a predetermined wavelength. As the predetermined wavelength, as anexample, the wavelength of 780 nm, or 650 nm is listed.

Further, the diffraction surface is formed on almost entire surface ofat least one optical surface of the optical element, means that thediffraction structure (relief) is provided on at least almost all of therange through which the light flux passes on the optical surface, andthat it is not the optical element in which the diffraction structure isprovided on a portion of the optical surface, for example, thediffraction structure is provided, for example, on only the peripheralportion. In this case, the range through which the light flux from thelight source passes to the information recording medium side, isdetermined by the aperture diaphragm used for the optical system or theoptical pickup apparatus. The range in which the diffraction surface isformed, ranges over almost all surface of the optical surface when it isviewed as the optical element single body provided with the diffractionsurface, however, generally, the optical surface is formed also on theperipheral portion through which the light flux does not pass, with acertain degree of the margin, therefore, when this portion is consideredbeing included in the optical surface as an available area as theoptical surface, it is preferable that the ratio of the area of thediffraction surface in the optical surface is at least more than half asthe optical element single body, and more preferably it is almost 100%.

Further, the optical system in Item 3 is characterized in that thespecific ordered of the diffracted ray respectively generatedselectively is the same ordered to the respective light having 2wavelengths which are different from each other.

According to Item 3, because the diffraction surface makes thediffraction efficiency of the diffracted ray of the same ordered,maximum to the respective light having at least 2 wavelengths, the lossof the light amount is smaller as compared to the case in which thediffraction surface makes the diffraction efficiency of the diffractedray of the different ordered, maximum.

Further, the optical system in Item 4 is characterized in that the sameordered diffracted ray is the first ordered diffracted ray. The firstordered diffracted ray may be +first ordered diffracted ray, or −firstordered diffracted ray.

According to Item 4, because the same ordered diffracted ray is thefirst ordered diffracted ray, the loss of the light amount is smaller ascompared to the case in which the same ordered diffracted ray is thehigher ordered diffracted ray than the first ordered diffracted ray.

Further, the optical system in Item 5 is characterized in that at least1 optical element of the optical element having the diffraction surfaceis a lens having the refraction power. The optical system in Item 5 maybe the optical system in which a fine structure (relief) for thediffraction is further formed on the surface of the lens having therefraction power. In this case, the enveloping surface of the finestructure for diffraction is the shape of diffraction surface of thelens. For example, so called blaze type diffraction surface is providedon at least one surface of the aspherical single lens objective lens,and it may be a lens, on the entire surface of which the annular bandwhose meridian cross section is the saw-toothed shape is provided.

According to Item 5, because the optical element having the diffractionsurface is the lens having the refraction power, both of the sphericalaberration and the chromatic aberration can be corrected, and the numberof parts can be reduced.

Further, the optical system in Item 6 is characterized in that the shapeof the diffraction surface of the lens is aspherical.

Further, the optical system in Item 7 is characterized in that the lensmakes the diffraction efficiency of the diffracted ray for the lighthaving a certain 1 wavelength which is the wavelength between themaximum wavelength and the minimum wavelength of the at least 2wavelengths which are different from each other, larger than thediffraction efficiency of the diffracted ray for the light having themaximum wavelength and the minimum wavelength.

Further, the optical system in Item 8 is characterized in that the lensmakes the diffraction efficiency of the diffracted ray for the lighthaving the maximum wavelength and the minimum wavelength of the at least2 wavelengths which are different from each other, larger than thediffraction efficiency of the diffracted ray for the light having thewavelength which is the wavelength between the maximum wavelength andthe minimum wavelength of the at least 2 wavelengths which are differentfrom each other.

Further, the optical system in Item 9 is characterized in that thepositive and negative signs of the diffraction effect which is added bythe diffraction surface of the lens are switched at least one time inthe direction separating from the optical axis perpendicularly to theoptical axis.

According to Item 9, because the positive and negative signs of thediffraction effect which is added by the diffraction surface of the lensare switched at least one time in the direction separating from theoptical axis perpendicularly to the optical axis, thereby, the variationof the wavelength of the spherical aberration can be suppressed.

Further, the optical system in Item 10 is characterized in that thediffraction effect which is added by the diffraction surface of the lensare switched one time from the negative to the positive in the directionseparating from the optical axis perpendicularly to the optical axis.

According to Item 10, because the diffraction power which is added bythe diffraction surface of the lens is switched one time from thenegative to the positive in the direction separating from the opticalaxis perpendicularly to the optical axis, thereby, when, for example,the parallel light flux enters into the objective lens in the CD systemand the DVD system, the influence on the spherical aberration due to thedifference of the thickness of the transparent substrate of theinformation recording medium can be effectively corrected without makingthe annular band pitch of the diffraction surface too small.

Relating to the diffraction power, particularly, in the case of theoptical element provided with the optical surface having the refractionaction and the diffraction action, in other words, in the case of theoptical element in which the diffraction surface is provided on theoptical surface having the refraction action, by the action of thediffraction surface, the action to converge or diverge the light flux isadded to the refraction action of the refraction surface which is thebase. In this case, when converging action is added to the light raywhich is in actual finite height, not limited to the paraxial area, inthe present invention, the following is defined: a predeterminedposition of the refraction surface has the positive diffraction power,and when the diverging action is added, it has the negative power.

The optical system in Item 11 is characterized in that the diffractionsurface is formed of a plurality of annular bands viewed from theoptical axis, and the plurality of annular bands are formed into almostconcentric circle-like one around the optical axis or a point near theoptical axis. That is, the diffraction surface of Item 11 is, forexample, as disclosed in Japanese Tokkaihei No. 6-242373, formedstepwise as the annular band, which shifts discretely in the directionin which the lens thickness is increased as being separated from theoptical axis.

Further, the optical system in Item 12 is characterized in that thephase difference function expressed by the power series showing eachposition of the plurality of annular bands has a factor except zero inat least 1 term except the 2nd power term.

According to Item 12, the spherical aberration can be controlled between2 different wavelengths. Herein, “can be controlled” means that thedifference of the spherical aberration can be made very small between 2wavelengths, and the difference necessary for the optical specificationcan be provided.

Further, the optical system in Item 13 is characterized in that thephase difference function expressed by the power series showing eachposition of the plurality of annular bands has a factor except zero in2nd power term.

According to Item 14, the correction of the chromatic aberration in theparaxial area can be effectively conducted.

Further, the optical system in Item 13 is characterized in that thephase difference function expressed by the power series showing eachposition of the plurality of annular bands does not include the 2ndpower term.

According to Item 14, because the phase difference function does notinclude the 2nd power term, the paraxial power of the diffractionsurface becomes 0, and only the term more than 4th power is used,thereby, the pitch of the diffraction annular band is not too small, andthe spherical aberration can be controlled.

The optical system in Item 15 is characterized in that the objectivelens is included in the more than 1 optical element, and to each of thelight having at least 2 wavelengths (wavelength λ) which are differentfrom each other, the wave front aberration on the image formationsurface is not more than 0.07 λrms in a predetermined numerical apertureon the image side of the objective lens.

According to Item 15, because the wave front aberration is not more than0.07 λrms, which is Mareshall's allowable value, in a predeterminednumerical aperture on the image side of the objective lens, thereby, anexcellent optical characteristic in which the spherical aberration isfully small, can be obtained.

The optical system in Item 16 is characterized in that, even if onewavelength λ₁ of at least 2 wavelengths which are different from eachother, varies within the range of ±10 nm, the wave front aberration onthe image formation surface is not more than 0.07 λ₁ rms in thepredetermined numerical aperture on the image side of the objectivelens.

According to Item 16, even if the wavelength λ₁ varies within the rangeof ±10 nm, an excellent optical characteristic in which the sphericalaberration is fully small, can be obtained.

Further, the optical system in Item 17 is characterized in that thelight having the wavelength λ₂ of at least 2 wavelengths which aredifferent from each other, and to the light having the anotherwavelength in which the numerical aperture on the image side of theobjective lens is larger than the predetermined numerical aperture ofthe light having the wavelength λ₂, the wave front aberration on theimage formation surface of the light having the wavelength λ₂ is notsmaller than 0.07 λ₂ rms in the predetermined numerical aperture of thelight having another wavelength.

According to Item 17, because the wave front aberration of the lighthaving the wavelength λ₂ is not smaller than 0.07 λ₂ rms in thepredetermined numerical aperture (which is not smaller than thepredetermined numerical aperture of the light having the wavelength λ₂)of the light having another wavelength, the appropriate spot diametercan be obtained for the light having the wavelength λ₂. That is, to thenumerical number in the actual use, the aberration is made almost zero,and for the outside portions thereof, the aberration is made into theflare, thereby, the predetermined effects can be obtained.

Further, the optical system in Item 18 is characterized in that thefront wave aberration of the light having the wavelength λ₂ on the imageformation surface is not less than 0.10 λ₂ rms in the predeterminednumerical aperture of the light having another wavelength.

According to Item 18, because the front wave aberration of the lighthaving the wavelength λ₂ is not less than 0.10 λ₂ rms in thepredetermined numerical aperture (which is larger than the predeterminednumerical aperture for the light having the wavelength λ₂) of the lighthaving another wavelength, the more appropriate spot diameter can beobtained for the light having the wavelength λ₂.

The optical system i Item 19 is characterized in that, when thepredetermined numerical aperture of the light having another wavelengthis NA1, and the predetermined numerical aperture of the light havingwavelength λ₂ is NA2, the optical system satisfies NA1>NA2>0.5 NA1.

Further, the optical system in Item 20 is characterized in that theparallel light flux for the light having at least 1 wavelength of atleast 2 wavelengths which are different from each other, is entered intothe objective lens, and non-parallel light flux for the light havinganother wavelength, is entered into the objective lens.

According to Item 20, because the parallel light flux for the lighthaving at least 1 wavelength of at least 2 wavelengths which aredifferent from each other, is entered into the objective lens, andnon-parallel light flux for the light having at least one otherwavelength, is entered into the objective lens, thereby, to thevariation of about 10 nm of the wavelengths of respective light havingat least 2 wavelengths, the variation of spherical aberration can besuppressed to a very small amount.

Further, the optical system in Item 21 is characterized in that theparallel light flux for the light having at least 2 wavelength of atleast 2 wavelengths which are different from each other, is entered intothe objective lens.

Further, the optical system in Item 22 is characterized in thatnon-parallel light flux for the light having at least 2 wavelengths, ofat least 2 wavelength which are different from each other, is enteredinto the objective lens.

Further, the optical system in Item 23 is characterized in that, whenthe longer wavelength of any 2 wavelengths of at least 2 wavelengthswhich are different from each other is defined as λ₃, and thepredetermined numerical aperture on the image side of the objective lensfor the light having the wavelength λ₃, is defined as NA, the axialchromatic aberration between the wavelength λ₃ and the shorterwavelength is not less than −λ₃/(2NA²) and not more than +λ₃/(2NA²).

According to Item 23, when the wavelength is switched, because the focusis hardly changed, the focus servo is not necessary, and the movementrange by the focus servo can be narrowed.

Further, the optical system in Item 24 is characterized in that thelight having at least 2 wavelengths which are different from each other,are respectively used for the information recording media whosetransparent substrate thickness are different from each other.

Further, the optical system in Item 25 is characterized in that at least2 wavelengths which are different from each other, are 3 wavelengthswhich are different from each other.

Further, the optical system in Item 26 is characterized in that, when 3wavelengths which are different from each other, are definedrespectively as λ1, λ2, and λ3 (λ1<λ2<λ3), and the predeterminednumerical apertures on the image side of the objective lens for each of3 wavelengths which are different from each other are respectivelydefined as NA1, NA2, and NA3, the following expressions are satisfied:0.60≦NA1, 0.60≦NA2, 0.40≦NA3≦0.50.

Further, the optical system in Item 27 is characterized in that a filterwhich can shield at least one portion of the light entered into theobjective lens at the outside of the smallest predetermined numericalaperture of the predetermined numerical aperture, is provided.

Further, the optical systems in Item 28 and Item 29 are characterized inthat the optical element having the diffraction surface is an objectivelens.

Further, the optical system in Item 30 is characterized in that theobjective lens comprises a piece of lens.

Further, the optical system in Item 31 is characterized in that thediffraction surface is provided on both surfaces of the objective lens.

Further, the optical system in Item 32 is characterized in that Abbe'snumber νd of the material of the objective lens is not smaller than 50.

According to Item 32, when the axial chromatic aberration is correctedfor the light source having 2 different wavelengths, the second orderedspectrum can be reduced.

Further, the optical system in Item 33 is characterized in that theobjective lens is made of plastics. According to Item 33, the opticalsystem which is a low cost and light in the weight, can be obtained.Further, the optical system in Item 34 is characterized in that theobjective lens is made of glass. According to Item 33 and Item 34, theoptical system which is very strong in the temperature change, can beobtained.

Further, the optical system in Item 35 is characterized in that theobjective lens has a resin layer in which the diffraction surface isformed, on the surface of the glass lens. According to Item 35, becausethe resin layer in which the diffraction structure can be easily formed,is provided on the glass lens, thereby, the optical system which is verystrong for the temperature change and advantageous in the cost, can beobtained.

Further, the optical system in Item 36 is characterized in that thedifference of wavelength between at least 2 wavelengths which aredifferent from each other, is not less than 80 nm.

Further, the optical system in Item 37 is characterized in that thedifference of wavelength between at least 2 wavelengths which aredifferent from each other, is not more than 400 nm.

Further, the optical system in Item 38 is characterized in that thedifference of wavelength between at least 2 wavelengths which aredifferent from each other, is not less than 100 nm and not more than 200nm.

Further, the optical system in Item 39 is characterized in that, to eachof the light having at least 2 wavelengths which are different from eachother, the diffraction efficiency of the specific ordereded diffractedray which is selectively generated, is higher by more than 10% than thediffraction efficiency of respective diffracted ray with the orderedexcept the specific ordered.

Further, the optical system in Item 40 is characterized in that, to eachof the light having at least 2 wavelengths which are different from eachother, the diffraction efficiency of the specific ordereded diffractedray which is selectively generated respectively, is higher by more than30% than the diffraction efficiency of respective diffracted ray withthe ordered except the specific ordered.

Further, the optical system in Item 41 is characterized in that, to eachof the light having at least 2 wavelengths which are different from eachother, the diffraction efficiency of the specific ordereded diffractedray which is selectively generated respectively, is more than 50%.

Further, the optical system in Item 42 is characterized in that, to eachof the light having at least 2 wavelengths which are different from eachother, the diffraction efficiency of the specific ordereded diffractedray which is selectively generated respectively, is more than 70%.

Further, the optical system in Item 43 is characterized in that, whenthe specific ordereded diffracted ray which is selectively generated,which has at least 2 wavelengths which are different from each other,focuses, because the diffracted surface is provided, the sphericalaberration is improved as compared to the case of no diffractionsurface.

Further, the optical system in Item 44 is characterized in that, to eachof the light (wavelength λ) having at least 2 wavelengths which aredifferent from each other, the wave front aberration on the imageformation surface of the specific ordereded diffracted ray which isselectively generated respectively, is not more than 0.07 λrms.

Further, the item 45 is a optical pickup apparatus characterized in thatit has above-described each optical system.

Further, the optical pickup apparatus in Item 46 which comprises: atleast 2 light sources which output the light having the wavelengthswhich are different from each other; an optical system including morethan 1 optical element by which the light from the light source isconverged onto the information recording medium; and a light detector todetect the transmitted light from the information recording medium orthe reflected light from the information recording medium, wherein atleast one optical element of the optical elements has the diffractionsurface which selectively generates the same ordereded diffracted ray asthe light having 2 different wavelengths outputted from at least 2 lightsources.

Further, the optical pickup apparatus in Item 47 which comprises: atleast 2 light sources which output the light having the wavelengthswhich are different from each other; an optical system including morethan 1 optical element by which the light from the light source isconverged onto the information recording medium; and a light detector todetect the transmitted light from the information recording medium orthe reflected light from the information recording medium, wherein thediffraction surface which selectively generates respectively specificordereded diffracted ray to respective light having 2 differentwavelengths outputted from at least 2 light sources, is formed on thealmost entire surface of at least one optical surface of at least oneoptical element of the optical elements.

Further, the optical pickup apparatus in Item 48 is characterized inthat at least one optical element of the optical elements having thediffraction surface described in Item 46 or Item 47 is a lens having thediffraction power.

Further, the optical pickup apparatus in Item 49 is characterized inthat the lens makes the diffraction efficiency of the diffracted ray tothe light having a certain wavelength between the maximum wavelength orthe minimum wavelength of 2 different wavelengths outputted from atleast 2 light sources, larger than the diffraction efficiency of thediffracted ray to the light having the maximum wavelength and theminimum wavelength.

Further, the optical pickup apparatus in Item 50 is characterized inthat the lens makes the diffraction efficiency of the diffracted ray tothe light having the maximum wavelength or the minimum wavelength of 2different wavelengths outputted from at least 2 light sources, largerthan the diffraction efficiency of the diffracted ray to the lighthaving a wavelength between the maximum wavelength and the minimumwavelength of at least 2 different wavelengths which are different fromeach other.

Further, the optical pickup apparatus in Item 51 is characterized inthat the lens has a flange portion on its outer periphery. Further, theoptical pickup apparatus in Item 52 is characterized in that the flangeportion has a surface extending in almost vertical direction to theoptical axis of the lens. By this flange portion, the lens can be easilyattached to the optical pickup apparatus, and when a surface extendingin almost vertical direction to the optical axis is provided, the moreaccurate attachment can be easily carried out.

Further, the optical pickup apparatus in Item 53 is characterized inthat the objective lens is included in at least more than 1 opticalelement, and the wave front aberration on the image formation surface toeach of the light (wavelength λ) having 2 different wavelengthsoutputted from at least 2 light sources, is not more than 0.07 λrms inthe predetermined numerical aperture on the image side of the objectivelens.

Further, the optical pickup apparatus in Item 54 is characterized inthat the objective lens is included in at least more than 1 opticalelement, and the wave front aberration on the image formation surface toeach of the light (wavelength λ) having 2 different wavelengthsoutputted from at least 2 light sources, is not more than 0.07 λrms inthe maximum numerical aperture on the image side of the objective lens.

Further, the optical pickup apparatus in Item 55 is characterized inthat, even when one wavelength λ₁ of 2 different wavelengths outputtedfrom at least 2 light sources, varies within the range of ±10 nm, thewave front aberration on the image formation surface is not more than0.07 λ₁ rms in the predetermined numerical aperture on the image side ofthe objective lens.

Further, the optical pickup apparatus in Item 56 is characterized inthat, to the light having the wavelength λ₂ of 2 different wavelengthsoutputted from at least 2 light sources, and the light having anotherwavelength in which the predetermined numerical aperture on the imageside of the objective lens is larger than the predetermined numericalaperture of the light having the wavelength λ₂, the wave frontaberration on the image formation surface of the light having thewavelength λ₂ is not less than 0.07 λ₂ rms in the predeterminednumerical aperture of the light having another wavelength.

Further, the image pick-up apparatus in Item 57 is characterized in thatthe wave front aberration on the image formation surface of the lighthaving the wavelength λ₂ is not less than 0.10 λ₂ rms in thepredetermined numerical aperture of the light having another wavelength.

Further, the image pick-up apparatus in Item 58 is characterized inthat, when the predetermined numerical aperture of the light havinganother wavelength is defined as NA1, and the predetermined numericalaperture of the light having the wavelength λ₂ is defined as NA2, thefollowing expression is satisfied: NA1>NA2>0.5×NA1.

Further, the image pick-up apparatus in Item 59 is characterized in thatthe parallel light flux for the light having at least 1 wavelength in 2different wavelengths outputted from at least 2 light sources, isentered into the objective lens, and the non-parallel light flux for thelight having at least another wavelength is entered into the objectivelens.

Further, the image pick-up apparatus in Item 60 is characterized in thatthe parallel light flux for the light having 2 different wavelengthsoutputted from at least 2 light sources, is entered into the objectivelens.

Further, the image pick-up apparatus in Item 61 is characterized in thatthe non-parallel light flux for the light having 2 different wavelengthsoutputted from at least 2 light sources, is entered into the objectivelens.

Further, the image pick-up apparatus in Item 62 is characterized inthat, when the longer wavelength in 2 different wavelengths outputtedfrom at least 2 light sources is defined as λ₃, and the predeterminednumerical aperture on the image side of the objective lens for the lighthaving the wavelength λ₃ is defined as NA, the axial chromaticaberration between the wavelength λ₃ and the shorter wavelength is notless than −λ₃/(2NA²) and not more than +λ₃/(2NA²).

Further, the image pick-up apparatus in Item 63 is characterized in thatthe light having 2 different wavelengths outputted from at least 2 lightsources are respectively used for the information recording media inwhich the thickness of the transparent substrates are different.

Further, the image pick-up apparatus in Item 64 is characterized in thatthe diffraction surface is formed of a plurality of annular bands viewedfrom the optical axis direction, and the plurality of annular bands areformed almost concentric circular around the optical axis or a point inthe vicinity of the optical axis, and between the pitch Pf of theannular band corresponding to the maximum numerical aperture on theimage side of the objective lens and the pitch Ph of the annular bandcorresponding to ½ numerical aperture in the maximum numerical aperture,the following relationship is established: 0.4≦|(Ph/Pf)−2|≦25.

According to Item 64, in the case of more than the lower limit of theabove relationship, the action of the diffraction to correct the higherordered spherical aberration is not weakened, and accordingly, thedifference of the spherical aberration between 2 wavelengths generatedby the difference of the thickness of the transparent substrate can becorrected by the action of the diffraction. Further, in the case of lessthan the upper limit, a portion in which the pitch of the diffractionannular band is too small, is hardly generated, thereby, a lens which isthe diffraction efficiency is high, can be produced. Further, theabove-described relational expression is preferably,0.8≦|(Ph/Pf)−2|≦6.0, and more preferably, 1.2≦|(Ph/Pf)−2|≦2.0.

Further, the optical pickup apparatus in Item 65 is characterized inthat at least 2 light sources are 3 light sources.

Further, the optical pickup apparatus in Item 66 is characterized inthat, when the light having 3 different wavelengths outputted from the 3light sources are respectively defined as λ1, λ2, and λ3 (λ1<λ2<λ3), andthe predetermined numerical apertures on the image side of the objectivelens for each of these 3 different wavelengths are defined as NA1, NA2,and NA3, the following relationships are satisfied: 0.60≦; NA1,0.60≦NA2, 0.40≦NA3≦0.50.

Further, the optical pickup apparatus in Item 67 is characterized inthat a filter by which at least one portion of the light entered intothe objective lens at the outside of the smallest numerical aperture inthe predetermined numerical apertures can be shielded, is provided.

Further, the optical pickup apparatus in Item 68 is characterized inthat an aperture limitation means is provided so that the predeterminednumerical aperture can be obtained for each of the light having the 2different wavelengths.

Further, the optical pickup apparatus in Item 69 is characterized inthat there is no aperture limitation by which the predeterminednumerical aperture can be obtained for one of the light having the 2different wavelengths. For example, concretely, the maximum numericalaperture has the aperture limitation, and the aperture limitation is notprovided for the smaller predetermined numerical aperture. Thereby, theaperture limitation means such as a filter having the wavelengthselectivity is made not necessary, therefore, the cost can be lower, andthe size can be reduced.

Further, the optical pickup apparatus in Item 70 is characterized inthat the objective lens is included in the more than 1 optical elements,and the objective lens is used in common when the light having thewavelengths which are different from each other, are respectivelyconverged onto the information recording medium.

Further, the optical pickup apparatus in Item 71 is characterized inthat a unit into which the at least 2 light sources and the object areintegrated, is driven at least parallelly to the main surface of theinformation recording medium.

Further, the optical pickup apparatus in Item 72 is characterized inthat the unit is vertically driven to the main surface of theinformation recording medium.

Further, Item 73 is a recording and reproducing apparatus which ischaracterized in that the optical pickup apparatus is mounted, and atleast either one of an audio or an image can be recorded or played back.

Further, a lens in Item 74 is characterized in that, in the lens whichis used for at least either one of the recording or reproducing of theinformation for the information recording medium, and has the refractionpower, and the diffraction surface on at least one of the opticalsurfaces, the positive and the negative signs of the diffraction poweradded from the diffraction surface are switched at least one time in thedirection separating from the optical axis vertically to the opticalaxis.

Further, the lens in Item 75 is characterized in that, in the lens inItem 74, the diffraction surface has a plurality of blazed diffractionannular bands, and its stepped portion is positioned at a separated sidefrom the optical axis in the diffraction annular band on the near sideto the optical axis, and in the diffraction annular band on theseparated side from the optical axis, its stepped portion is positionedon a near side to the optical axis. Further, the lens in Item 76 ischaracterized in that the diffraction surface has a plurality of blazeddiffraction annular bands, and its stepped portion is positioned on anear side to the optical axis in the diffraction annular band on thenear side to the optical axis, and in the diffraction annular band onthe separated side from the optical axis, its stepped portion ispositioned on a separated side from the optical axis.

Further, the Item 77 is an optical element which can be applied to theoptical system for recording and/or reproducing of the information intoor from the information recording medium, the optical element ischaracterized in that, when it is used in the optical system forrecording and/or reproducing of the information into or from theinformation recording medium, in which the light having at least 2wavelengths which are different from each other are used, it has thediffraction surface to selectively generate the same orderededdiffracted ray to the light having at least 2 wavelengths which aredifferent from each other.

Further, Item 78 is a lens which can be applied as an objective lens inthe optical system for recording and/or reproducing of the informationinto or from the information recording medium, the lens is characterizein that, when it is used as the objective lens in the optical system forrecording and/or reproducing of the information into or from theinformation recording medium, in which the light having at least 2wavelengths which are different from each other are used, it has thediffraction surface to selectively generate the diffraction efficiencyof the same ordereded diffracted ray to the light having at least 2wavelengths which are different from each other.

Further, Item 79 is an optical element which can be applied in theoptical system for recording and/or reproducing of the information intoor from the information recording medium, the optical element ischaracterized in that, when it is used in the optical system forrecording and/or reproducing of the information into or from theinformation recording medium, in which the light having at least 2wavelengths which are different from each other are used, thediffraction surface to selectively generate the specific orderededdiffracted ray to the light having at least 2 wavelengths which aredifferent from each other, is formed on almost entire surface of atleast one optical surface.

Further, Item 80 is a lens which can be applied as an objective lens inthe optical system for recording and/or reproducing of the informationinto or from the information recording medium, the lens is characterizein that, when it is used as the objective lens in the optical system forrecording and/or reproducing of the information into or from theinformation recording medium, in which the light having at least 2wavelengths which are different from each other are used, thediffraction surface to selectively generate the specific orderededdiffracted ray to the light having at least 2 wavelengths which aredifferent from each other, is formed on almost entire surface of atleast one optical surface.

Further, a diffraction optical system for the optical disk in Item 81 ischaracterized in that, in the recording and reproducing optical systemwhich has 2 light source having different wavelengths and records andplays back by the same optical system, the optical system includes theoptical surface on which the diffraction annular band lens is providedon the refraction surface, and the aberration generated by thedifference of the wavelength on the refraction surface and theaberration generated by the diffraction annular band lens are cancelled,and the diffracted ray used for the canceling is the same orderededdiffracted ray to the wavelengths of 2 light source.

As described above, this diffraction optical system is characterized inthat it includes the optical surface on which the diffraction annularband lens is provided on the refraction surface, and to each of thelight sources having 2 different wavelengths, a certain 1 same orderededdiffracted ray and the spherical aberration by the diffraction surfaceare cancelled, thereby, these are corrected to no aberration, which isalmost equal to the diffraction limit. The same ordereded diffracted rayis preferably first ordered diffracted ray.

A method to make the same ordereded diffracted ray to correspond to eachwavelength of 2 light sources as the present invention, has an advantagein which totally the loss of the light amount is smaller, as compared tothe case in which the diffracted ray of the different ordered is made tocorrespond to. For example, in the case where 2 wavelengths of 780 nmand 635 nm are used, when the first ordered diffracted ray is used forthe light of both wavelengths, totally the loss of the light amount issmaller than the case in which the first ordered diffracted ray is usedfor one wavelength, and the zero ordered diffracted ray is used for theother wavelength. Further, in the case where the same ordered diffractedray is used for the light of both wavelength, when the first ordereddiffracted ray is used, the loss of the light amount is smaller than thecase where high ordereded diffracted ray is used.

Further, a diffraction optical system for an optical disk in Item 82 ischaracterized in that the canceled aberration is the sphericalaberration and/or the chromatic aberration.

Further, a diffraction optical system for an optical disk in Item 83 ischaracterized in that the diffracted ray of the same ordered is thefirst ordered diffracted ray.

Further, a diffraction optical system for an optical disk in Item 84 ischaracterized in that the light sources of 2 different wavelengthscorrespond to the optical disks whose transparent substrate thicknessare respectively different.

Further, a diffraction optical system for an optical disk in Item 85 ischaracterized in that the wavelength of the light source of the shorterwavelength in 2 wavelengths which are different from each other is notlarger than 700 nm.

Further, a diffraction optical system for an optical disk in Item 86 ischaracterized in that the wavelength of the light source of the longerwavelength in 2 wavelengths which are different from each other is notshorter than 600 nm.

Further, a diffraction optical system for an optical disk in Item 87 ischaracterized in that, in the diffraction annular band lens, the phasefunction expressing the position of the annular band includes factors ofterms except second power of power series.

Further, a diffraction optical system for an optical disk in Item 88 ischaracterized in that the optical refraction surface is aspherical.

Further, a diffraction optical system for an optical disk in Item 89 ischaracterized in that, to the light sources of 2 different wavelengthswhich are different from each other, the diffraction efficiency of thediffracted ray is maximum at the almost intermediate wavelength thereof.

Further, a diffraction optical system for an optical disk in Item 90 ischaracterized in that, to the light sources of 2 different wavelengthswhich are different from each other, the diffraction efficiency of thediffracted ray is maximum at one of wavelengths of the light sources.

Further, a diffraction optical system for an optical disk in Item 91 ischaracterized in that, in the diffraction annular band lens on theoptical surface, the spherical aberration is corrected to an undervalue, and in the aspherical surface of the optical surface, thespherical aberration is corrected to an over value.

Further, in a diffraction optical system for an optical disk in Item 91,when the objective lens is used for the parallel light incidence forboth of, for example, CD system (for example, the wavelength is 780 nm,the substrate thickness is 1.2 mm) and DVD system (for example, thewavelength is 650 nm, the substrate thickness is 0.6 mm), in the CDsystem, because the thickness of the substrate is thick, the sphericalaberration has an over value compared to that of DVD system, however,because this spherical aberration is corrected by the difference of thewavelength of the diffraction lens, the spherical aberration of thediffraction lens is made under. Incidentally, in this case, in the longwavelength of the CD system, the spherical aberration of the diffractionlens becomes largely under, therefore, the influence due to thethickness of the substrate is corrected. In the aspherical surface, theinfluence of the difference of the substrate thickness is not corrected,and in both of the CD system and DVD system, the spherical aberration isoverly corrected to almost the same degree. In the above description, itis utilized that, when high ordered terms of the diffraction are used,the wave motion of the spherical aberration can be largely controlled.

Further, in a diffraction optical system for an optical disk in Item 92,its difference of the wavelength is not less than 80 nm in the lightsources having 2 different wavelengths.

Further, a diffraction optical system for an optical disk in Item 93 ischaracterized in that, in the objective lens optical system of theoptical disk, when the diffraction annular band lens is provided on theoptical surface, the axial chromatic aberration of a certain one of thesame ordereded diffracted ray is corrected to each of the light sourceshaving 2 different wavelengths.

Further, a diffraction optical system for an optical disk in Item 94 ischaracterized in that the difference of the wavelengths of the lightsources having 2 different wavelengths is not less than 80 nm, and thediffraction optical system has a single objective lens which satisfiesthe following relationship: νd>50, where, νd is Abbe's number of theglass material of the objective lens.

Further, a diffraction optical system for an optical disk in Item 95 ischaracterized in that, in the lens performance to 2 differentwavelengths, either one is no-aberration up to the aperture in thepractical use, and in its outside portion, the aberration is made aflare.

Further, a diffraction optical system for an optical disk in Item 96 ischaracterized in that, in the lens performance to 2 differentwavelengths, when the numerical number to the wavelength which isno-aberration in the open aperture, is defined as NA1, and the numericalaperture of the other wavelength in the practical use is defined as NA2,the following relationship is satisfied: NA1>NA2>0.5×NA1.

Further, a diffraction optical system for an optical disk in Item 97 ischaracterized in that the thickness of the optical disk to the 2different wavelengths is different.

Further, a optical pickup apparatus in Item 98 is a optical pickupapparatus used for the recording and reproducing optical system whichhas at least more than 2 light sources having the different wavelengths,and in which the divergent light flux from each of light sources is usedfor recording the information onto and/or reproducing the information onthe information recording surface of the optical information recordingmedium by the same one objective lens through the transparent substrate,the optical pickup apparatus in Item 98 is characterized in that theobjective lens includes the optical surface in which the ring band-likediffraction surface is provided on the refraction surface, and to atleast 1 light source, the light flux transmitted through the objectivelens and the transparent substrate has the diffraction limit performanceat the best image point.

Herein, the diffraction limit performance means that the wave frontaberration is measured, and the root mean square value (rms value) ofthe wave front aberration of the entire light flux is not more than 0.07times of the wavelength which is Mareshal's allowance. Further, theaperture in the practical use means the numerical aperture which isregulated by respective standards of the optical information recordingmedium, and corresponds to the numerical aperture of the objective lensof the diffraction limit performance by which the spot diameternecessary for recording or reproducing of the information to respectiveoptical information recording media, can be obtained.

As described above, because the numerical aperture in the practical useis regulated to the optical information recording medium, the numericalaperture on the optical information recording medium side of the actuallight flux passing through the optical system of the pick-up apparatusmay be larger than the numerical aperture in the practical use.

Further, in the present invention, it may be preferable that the maximumnumerical aperture preferably means the maximum one in the numericalaperture in the practical use. That is, in the case of the pick-upapparatus interchangeably used for a plurality of optical informationrecording media, a plurality of numerical apertures in the practical useare defined, and it may be preferable that the maximum one in thesenumerical apertures is defined as the maximum numerical aperture.Further, a predetermined numerical aperture and necessary numericalaperture are the same meaning as the numerical aperture in the practicaluse.

Incidentally, in the case where the information is recorded onto orplayed back from the optical information recording medium, when thelight source having the different wavelength from that of the lightsource regulated by the standard is used in the actual optical pickupapparatus, the actually used numerical aperture is set so that the ratioof the regulated wavelength and the regulated numerical aperture, andthe ratio of the actually used wavelength and the actually usednumerical aperture, becomes constant. As an example, in the CD, when thelight source with 780 nm wavelength in the standard is used, thenumerical aperture is 0.45, however, when the light source with 650 nmwavelength is used, the numerical aperture is 0.38.

Further, a optical pickup apparatus in Item 99 is a optical pickupapparatus used for the recording and reproducing optical system whichhas at least more than 2 light sources having the different wavelengths,and in which the divergent light flux from each of light sources is usedfor recording the information onto and/or reproducing the information onthe information recording surface of the optical information recordingmedium by the same one objective lens through the transparent substrate,the optical pickup apparatus in Item 99 is characterized in that theobjective lens includes the optical surface in which the ring band-likediffraction surface is provided on the refraction surface, and to atleast 1 light source, the light flux transmitted through the objectivelens and the transparent substrate has the diffraction limit performanceat the best image point, and to at least 1 light source, in the lightflux transmitted through the objective lens and the transparentsubstrate, the light flux up to the aperture in the practical use hasthe diffraction limit performance at the best image point, and the ringband-like diffraction surface is provided so that the outside portionthereof becomes the flare.

Further, the optical pickup apparatus in Item 100 is characterized inthat the above-described apparatus has at least 3 light sources havingdifferent wavelengths.

Further, the optical pickup apparatus in Item 101 is characterized inthat the above-described apparatus includes the optical surface on whichat least more than 2 ring band-like diffraction surfaces are provided.

Further, the optical pickup apparatus in Item 102 is characterized inthat the above-described apparatus includes a ring band-like filter toshield a portion of the light flux outside of the actually used aperturein the light flux entering into the objective lens.

Further, the optical pickup apparatus in Item 103 is characterized inthat, in the above-described apparatus, the unit including the lightsource and the objective lens, is driven parallely at least to theoptical information recording medium.

Further, the optical pickup apparatus in Item 104 is characterized inthat, in the above-described apparatus, the unit including the lightsource and the objective lens, is further driven vertically to theoptical information recording medium.

Further, the invention according to Item 105 is an audio and/or imagerecording, and/or an audio and/or image reproducing apparatuscharacterized in that the above-described optical pickup apparatus ismounted.

Further, an objective lens in Item 106 is an objective lens used for therecording and reproducing optical system which has at least more than 2light sources having the different wavelengths, and in which thedivergent light flux from each of light sources is used for recordingthe information onto and/or reproducing the information on theinformation recording surface of the optical information recordingmedium by the same one objective lens through the transparent substrate,the objective lens is characterized in that it includes the opticalsurface in which the ring band-like diffraction surface is provided onthe refraction surface, and to at least 1 light source, the light fluxtransmitted through the objective lens and the transparent substrate hasthe diffraction limit performance at the best image point.

Further, an objective lens in Item 107 is an objective lens used for therecording and reproducing optical system which has at least more than 2light sources having the different wavelengths, and in which thedivergent light flux from each of light sources is used for recordingthe information onto and/or reproducing the information on theinformation recording surface of the optical information recordingmedium by the same one objective lens through the transparent substrate,the objective lens is characterized in that it includes the opticalsurface in which the ring band-like diffraction surface is provided onthe refraction surface, and to at least 1 light source, the light fluxtransmitted through the objective lens and the transparent substrate hasthe diffraction limit performance at the best image point, and to atleast 1 light source, in the light flux transmitted through theobjective lens and the transparent substrate, the light flux up to theaperture in the practical use has the diffraction limit performance atthe best image point, and the ring band-like diffraction surface isprovided so that the outside portion thereof becomes the flare.

Further, the optical pickup apparatus in Item 108 in which the lightflux emitted from the light source is converged onto the informationrecording surface by the light converging optical system including theobjective lens through the transparent substrate of the opticalinformation recording medium, and which has the first light sourcehaving the wavelength λ1 to record/reproducing the first opticalinformation recording medium, the second light source having thewavelength λ2 to record/reproducing the second optical informationrecording medium, and the third light source having the wavelength λ3 torecord/reproducing the third optical information recording medium, whosewavelengths are different from each other, and records and plays backthe optical information recording medium, the optical pickup apparatusis characterized in that, on at least one surface of the objective lens,the diffraction surface by which the spherical aberration is correctedto almost the same degree as the diffraction limit or smaller than it bya certain same ordereded diffracted ray to each of optical informationrecording media, is formed.

Further, the optical pickup apparatus in Item 109 in which the lightflux emitted from the light source is converged onto the informationrecording surface by the light converging optical system including theobjective lens through the transparent substrate of the opticalinformation recording medium, and which has the first light sourcehaving the wavelength λ1 to record/reproducing the first opticalinformation recording medium, the second light source having thewavelength λ2 to record/reproducing the second optical informationrecording medium, and the third light source having the wavelength λ3 torecord/reproducing the third optical information recording medium, whosewavelengths are different from each other, and records and plays backthe optical information recording medium, the optical pickup apparatusis characterized in that, on at least one surface of the objective lens,a certain same ordereded diffracted ray is used for each of opticalinformation recording media, and for at least one optical informationrecording medium, the aberration up to the aperture in the practical useis made to almost the same degree as the diffraction limit or smallerthan it, and the aberration in a portion outside the aperture is made tothe flare.

In the optical pickup apparatus in Item 109 to record and/or reproducethe optical information recording medium, the objective lens formed thediffraction surface uses a certain same ordereded diffracted ray foreach of optical information recording media, and for at least oneoptical information recording medium, the aberration up to the aperturein the practical use is made to almost the same degree as thediffraction limit or smaller than it, and the aberration in a portionoutside the aperture is made to the flare.

Further, as will be described in following Items, it is preferable thatthe diffraction surface is formed on both surfaces of the objectivelens, and the diffracted ray is the first ordered diffracted ray. Thefollowing is characterized: the diffraction surface is formed to ringband-like around the optical axis of the objective lens, and the phasefunction to express the position of the annular band includes factors ofterms except 2 power term in the power series, however, the phasefunction may include the 2 power term in the power series, or may notinclude it. Further, it is preferable that, in the diffraction surface,the diffraction efficiency of the diffracted ray is maximum in thewavelength of both ends or of intermediate area, to each of the firstlight source, the second light source, and the third light source.Further, the objective lens has at least one surface which isaspherical, and the spherical aberration is corrected to under on thediffraction surface, and the spherical aberration is corrected to overon the aspherical surface, thereby, the above-described function can beprovided.

Further, the optical pickup apparatus in Item 110 is characterized inthat the diffraction surface is formed on both sides of the objectivelens.

Further, the optical pickup apparatus in Item 111 is characterized inthat the same ordereded diffracted ray is the first ordered diffractedray.

Further, the optical pickup apparatus in Item 112 is characterized inthat the diffraction surface is formed to ring band-like around theoptical axis of the objective lens, and the phase function to expressthe position of the annular band includes the factors of terms exceptthe second power term in the power series.

Further, the optical pickup apparatus in Item 113 is characterized inthat the diffraction surface is formed to ring band-like around theoptical axis of the objective lens, and the phase function to expressthe position of the annular band includes the factor of the second powerterm in the power series.

Further, the optical pickup apparatus in Item 114 is characterized inthat the diffraction surface is formed to ring band-like around theoptical axis of the objective lens, and the phase function to expressthe position of the annular band does not include the factor of thesecond power term in the power series.

Further, the optical pickup apparatus in Item 115 is characterized inthat the diffraction efficiency of the diffracted ray is maximum in thewavelength of both ends or of intermediate area, to each of the firstlight source, the second light source, and the third light source.

Further, the optical pickup apparatus in Item 116 is characterized inthat at least one surface of the objective lens is aspherical, and thespherical aberration is corrected to under on the diffraction surface,and the spherical aberration is corrected to over on the asphericalsurface.

Further, the invention in Item 117 is an audio and/or image writing,and/or an audio and/or image reproducing apparatus, which ischaracterized in that the optical pickup apparatus described in any ofItems 108–116 having the first light source, the second light source andthe third light source, is mounted.

Further, an objective lens in Item 118 used for the optical pickupapparatus in which the light flux emitted from the light source isconverged onto the information recording surface by the light convergingoptical system through the transparent substrate of the opticalinformation recording medium, and which has the first light sourcehaving the wavelength λ1 to record/reproducing the first opticalinformation recording medium, the second light source having thewavelength λ2 to record/reproducing the second optical informationrecording medium, and the third light source having the wavelength λ3 torecord/reproducing the third optical information recording medium, whosewavelengths are different from each other, and records and plays backthe optical information recording medium, the objective lens ischaracterized in that, on at least one surface of the objective lens,the diffraction surface is formed, in which the spherical aberration iscorrected by a certain same ordereded diffracted ray for each of opticalinformation recording media, to almost the same degree as thediffraction limit or smaller than it.

Further, an objective lens in Item 119 used for the optical pickupapparatus in which the light flux emitted from the light source isconverged onto the information recording surface by the light convergingoptical system through the transparent substrate of the opticalinformation recording medium, and which has the first light sourcehaving the wavelength λ1 to record/reproducing the first opticalinformation recording medium, the second light source having thewavelength λ2 to record/reproducing the second optical informationrecording medium, and the third light source having the wavelength λ3 torecord/reproducing the third optical information recording medium, whosewavelengths are different from each other, and records and plays backthe optical information recording medium, the objective lens ischaracterized in that, on at least one surface of the objective lens, acertain same ordereded diffracted ray is used for each of opticalinformation recording media, and to at least one optical informationrecording medium, the spherical aberration is corrected up to theaperture in the practical use to almost the same degree as thediffraction limit or smaller than it, and to the portion outside it, theaberration is made to the flare.

Further, the optical pickup apparatus in Item 120 in which the lightflux emitted from the light source is converged onto the informationrecording surface by the light converging optical system through thetransparent substrate of the optical information recording medium, andwhich has the first light source having the wavelength λ1 torecord/reproducing the first optical information recording medium, thesecond light source having the wavelength λ2 to record/reproducing thesecond optical information recording medium, and the third light sourcehaving the wavelength λ3 to record/reproducing the third opticalinformation recording medium, whose wavelengths are different from eachother, and records and plays back the optical information recordingmedium, the optical pickup apparatus is characterized in that, on atleast one surface of the light converging optical system, thediffraction surface is formed, in which the spherical aberration iscorrected by a certain same ordereded diffracted ray for each of opticalinformation recording media, to almost the same degree as thediffraction limit or smaller than it.

Further, the optical pickup apparatus in Item 121 in which the lightflux emitted from the light source is converged onto the informationrecording surface by the light converging optical system through thetransparent substrate of the optical information recording medium, andwhich has the first light source having the wavelength λ1 torecord/reproducing the first optical information recording medium, thesecond light source having the wavelength λ2 to record/reproducing thesecond optical information recording medium, and the third light sourcehaving the wavelength λ3 to record/reproducing the third opticalinformation recording medium, whose wavelengths are different from eachother, and records and plays back the optical information recordingmedium, the optical pickup apparatus is characterized in that, on atleast one surface of the light converging optical system, thediffraction surface is provided, in which a certain same orderededdiffracted ray is used for each of optical information recording media,and for at least one optical information recording medium, theaberration is corrected to almost the same degree as the diffractionlimit or smaller than it, up to the aperture in the practical use, andto the portion outside it, the aberration is made to the flare.

Further, the optical pickup apparatus in Item 122 has: the first lightsource with the wavelength λ1, the second light source with thewavelength λ2 (λ2≠λ1); the objective lens which has the diffractionpattern on at least one surface, and converges the light flux from eachof the light sources onto the information recording surface of theoptical information recording medium through the transparent substrate;and the light detector to receive the reflected light of the emittedlight flux from the first light source and the second light source fromthe optical information recording medium, and when, at least, them-ordered diffracted ray (m is an integer except 0) from the diffractionpattern of the objective lens of the light flux from the first lightsource is used, the first optical information recording medium, in whichthe thickness of the transparent substrate is t1, is recorded and/orplayed back, and when, at least, the n-th ordered diffracted ray (n=m)from the diffraction pattern of the objective lens of the light fluxfrom the first light source is used, the second optical informationrecording medium, in which the thickness of the transparent substrate ist2 (t2≠t1), is recorded and/or played back.

Further, the optical pickup apparatus in Item 123 is a optical pickupapparatus used in the relationship in which the wavelengths λ1 and λ2 ofthe first and the second light sources are λ1<λ2, and the thickness ofthe transparent substrate t1 and t2 are t1<t2 the optical pickupapparatus is characterized in that the m-ordered and n-th ordereddiffracted ray are both +first ordered diffracted ray.

Further, the optical pickup apparatus in Item 124 is a optical pickupapparatus used in the relationship in which the wavelengths λ1 and λ2 ofthe first and the second light sources are λ1<λ2, and the thickness ofthe transparent substrate t1 and t2 are t1>t2 the optical pickupapparatus is characterized in that the m-ordered and n-th ordereddiffracted ray are both −first ordered diffracted ray.

Further, the optical pickup apparatus in Item 125 is characterized inthat, in the apparatus in Item 122, when the necessary numericalaperture on the optical information recording medium side of theobjective lens required for recording and/or reproducing the firstoptical information recording medium in which the thickness of thetransparent substrate is t1, by the first light source with thewavelength λ1, is defined as NA1, and the necessary numerical apertureon the optical information recording medium side of the objective lensrequired for recording and/or reproducing the second optical informationrecording medium in which the thickness of the transparent substrate ist2 (t2>t1), by the second light source with the wavelength λ2 (λ2>λ1),is defined as NA2 (NA2<NA1), the diffraction pattern provided on atleast one surface of the objective lens is the rotation symmetry to theoptical axis, and +first ordered diffracted ray from the circumferencemost separated from the optical axis of the diffraction pattern of theobjective lens of the light flux from the first light source isconverted into the light flux whose numerical aperture on the opticalinformation recording medium side is NAH1, and +first ordered diffractedray from the circumference nearest to the optical axis side of thediffraction pattern of the objective lens of the light flux from thefirst light source is converted into the light flux whose numericalaperture on the optical information recording medium side is NAL1, andthe following relationship is satisfied:NAH1<NA1, 0≦NAL1≦NA2.

Further, the optical pickup apparatus in Item 126 is characterized inthat, in the apparatus in Item 122, when the necessary numericalaperture on the optical information recording medium side of theobjective lens required for recording and/or reproducing the firstoptical information recording medium in which the thickness of thetransparent substrate is t1, by the first light source with thewavelength λ1, is defined as NA1, and the necessary numerical apertureon the optical information recording medium side of the objective lensrequired for recording and/or reproducing the second optical informationrecording medium in which the thickness of the transparent substrate ist2 (t2>t1), by the second light source with the wavelength λ2 (λ2>λ1),is defined as NA2 (NA2>NA1), the diffraction pattern provided on atleast one surface of the objective lens is the rotation symmetry to theoptical axis, and +first ordered diffracted ray from the circumferencemost separated from the optical axis of the diffraction pattern of theobjective lens of the light flux from the first light source isconverted into the light flux whose numerical aperture on the opticalinformation recording medium side is NAH1, and +first ordered diffractedray from the circumference nearest to the optical axis side of thediffraction pattern of the objective lens of the light flux from thefirst light source is converted into the light flux whose numericalaperture on the optical information recording medium side is NAL1, andthe following relationship is satisfied:NAH1<NA2, 0≦NAL1≦NA1.

Further, the optical pickup apparatus in Item 127 is characterized inthat, in the apparatus in Item 122, when the necessary numericalaperture on the optical information recording medium side of theobjective lens required for recording and/or reproducing the firstoptical information recording medium in which the thickness of thetransparent substrate is t1, by the first light source with thewavelength λ1, is defined as NA1, and the necessary numerical apertureon the optical information recording medium side of the objective lensrequired for recording and/or reproducing the second optical informationrecording medium in which the thickness of the transparent substrate ist2 (t2<t1), by the second light source with the wavelength λ2 (λ2>λ1),is defined as NA2 (NA2<NA1), the diffraction pattern provided on atleast one surface of the objective lens is the rotation symmetry to theoptical axis, and −first ordered diffracted ray from the circumferencemost separated from the optical axis of the diffraction pattern of theobjective lens of the light flux from the first light source isconverted into the light flux whose numerical aperture on the opticalinformation recording medium side is NAH1, and −first ordered diffractedray from the circumference nearest to the optical axis side of thediffraction pattern of the objective lens of the light flux from thefirst light source is converted into the light flux whose numericalaperture on the optical information recording medium side is NAL1, andthe following relationship is satisfied:NAH1<NA1, 0≦NAL1≦NA2.

Further, the optical pickup apparatus in Item 128 is characterized inthat, in the apparatus in Item 122, when the necessary numericalaperture on the optical information recording medium side of theobjective lens required for recording and/or reproducing the firstoptical information recording medium in which the thickness of thetransparent substrate is t1, by the first light source with thewavelength λ1, is defined as NA1, and the necessary numerical apertureon the optical information recording medium side of the objective lensrequired for recording and/or reproducing the second optical informationrecording medium in which the thickness of the transparent substrate ist2 (t2<t1), by the second light source with the wavelength λ2 (λ2>λ1),is defined as NA2 (NA2>NA1), the diffraction pattern provided on atleast one surface of the objective lens is the rotation symmetry to theoptical axis, and −first ordered diffracted ray from the circumferencemost separated from the optical axis of the diffraction pattern of theobjective lens of the light flux from the first light source isconverted into the light flux whose numerical aperture on the opticalinformation recording medium side is NAH1, and −first ordered diffractedray from the circumference nearest to the optical axis side of thediffraction pattern of the objective lens of the light flux from thefirst light source is converted into the light flux whose numericalaperture on the optical information recording medium side is NAL1, andthe following relationship is satisfied:NAH1<NA2, 0≦NAL1≦NA1.

Further, the optical pickup apparatus in Item 129 is characterized inthat, in the apparatus in Item 125, in the light flux from the firstlight source, the light converging position of the light flux whosenumerical aperture is not more than NA1 when the light flux passesthrough the objective lens and which does not pass through thediffraction pattern, is almost the same as the light converging positionof the light flux which passes through the diffraction pattern.

Further, the optical pickup apparatus in Item 130 is characterized inthat, in the apparatus in Item 126, in the light flux from the secondlight source, the light converging position of the light flux whosenumerical aperture is not more than NA2 when the light flux passesthrough the objective lens and which does not passes through thediffraction pattern, is almost the same as the light converging positionof the light flux which passes through the diffraction pattern.

Further, the optical pickup apparatus in Item 131 is characterized inthat, in the apparatus in Item 127, in the light flux from the firstlight source, the light converging position of the light flux whosenumerical aperture is not more than NA1 when the light flux passesthrough the objective lens and which does not pass through thediffraction pattern, is almost the same as the light converging positionof the light flux which passes through the diffraction pattern.

Further, the optical pickup apparatus in Item 132 is characterized inthat, in the apparatus in Item 128, in the light flux from the secondlight source, the light converging position of the light flux whosenumerical aperture is not more than NA2 when the light flux passesthrough the objective lens and which does not passes through thediffraction pattern, is almost the same as the light converging positionof the light flux which passes through the diffraction pattern.

Further, the optical pickup apparatus in Item 133 is characterized inthat, in the apparatus in Item 129, +first ordered diffracted ray fromthe circumference most separated from the optical axis of thediffraction pattern of the objective lens of the light flux from thesecond light source is converted into the light flux whose numericalaperture on the optical information recording medium side is NAH2, and+first ordered diffracted ray from the circumference nearest to theoptical axis of the diffraction pattern of the objective lens of thelight flux from the second light source is converted into the light fluxwhose numerical aperture on the optical information recording mediumside is NAL2, and the spherical aberration of the light flux whichpasses through the objective lens is set such that, in the light fluxfrom the first light source, the light flux whose numerical aperture isnot more than NA1 when the light flux passes through the objective lensis used and spots are converged on the information recording surface ofthe optical information recording medium so that recording and/orreproducing of the first optical information recording medium can beconducted, and in the light flux from the second light source, the lightflux whose numerical aperture is not more than NAH2 when the light fluxpasses through the objective lens is used and spots are converged on theinformation recording surface of the optical information recordingmedium so that recording and/or reproducing of the second opticalinformation recording medium can be conducted.

Further, the optical pickup apparatus in Item 134 is characterized inthat, in the apparatus in Item 130, +first ordered diffracted ray fromthe circumference most separated from the optical axis of thediffraction pattern of the objective lens of the light flux from thesecond light source is converted into the light flux whose numericalaperture on the optical information recording medium side is NAH2, and+first ordered diffracted ray from the circumference nearest to theoptical axis of the diffraction pattern of the objective lens of thelight flux from the second light source is converted into the light fluxwhose numerical aperture on the optical information recording mediumside is NAL2, and the spherical aberration of the light flux whichpasses through the objective lens is set such that, in the light fluxfrom the first light source, the light flux whose numerical aperture isnot more than NAH1 when the light flux passes through the objective lensis used and spots are converged on the information recording surface ofthe optical information recording medium so that recording and/orreproducing of the first optical information recording medium can beconducted, and in the light flux from the second light source, the lightflux whose numerical aperture is not more than NA2 when the light fluxpasses through the objective lens is used and spots are converged on theinformation recording surface of the optical information recordingmedium so that recording and/or reproducing of the second opticalinformation recording medium can be conducted.

Further, the optical pickup apparatus in Item 135 is characterized inthat, in the apparatus in Item 131, −first ordered diffracted ray fromthe circumference most separated from the optical axis of thediffraction pattern of the objective lens of the light flux from thesecond light source is converted into the light flux whose numericalaperture on the optical information recording medium side is NAH2, and−first ordered diffracted ray from the circumference nearest to theoptical axis of the diffraction pattern of the objective lens of thelight flux from the second light source is converted into the light fluxwhose numerical aperture on the optical information recording mediumside is NAL2, and the spherical aberration of the light flux whichpasses through the objective lens is set such that, in the light fluxfrom the first light source, the light flux whose numerical aperture isnot more than NA1 when the light flux passes through the objective lens,is used, and spots are converged on the information recording surface ofthe optical information recording medium so that recording and/orreproducing of the first optical information recording medium can beconducted, and in the light flux from the second light source, the lightflux whose numerical aperture is not more than NAH2 when the light fluxpasses through the objective lens, is used, and spots are converged onthe information recording surface of the optical information recordingmedium so that recording and/or reproducing of the second opticalinformation recording medium can be conducted.

Further, the optical pickup apparatus in Item 136 is characterized inthat, in the apparatus in Item 132, −first ordered diffracted ray fromthe circumference most separated from the optical axis of thediffraction pattern of the objective lens of the light flux from thesecond light source is converted into the light flux whose numericalaperture on the optical information recording medium side is NAH2, and−first ordered diffracted ray from the circumference nearest to theoptical axis of the diffraction pattern of the objective lens of thelight flux from the second light source is converted into the light fluxwhose numerical aperture on the optical information recording mediumside is NAL2, and the spherical aberration of the light flux whichpasses through the objective lens is set such that, in the light fluxfrom the first light source, the light flux whose numerical aperture isnot more than NAH1 when the light flux passes through the objective lensis used and spots are converged on the information recording surface ofthe optical information recording medium so that recording and/orreproducing of the first optical information recording medium can beconducted, and in the light flux from the second light source, the lightflux whose numerical aperture is not more than NA2 when the light fluxpasses through the objective lens is used and spots are converged on theinformation recording surface of the optical information recordingmedium so that recording and/or reproducing of the second opticalinformation recording medium can be conducted.

Further, the optical pickup apparatus in Item 137 is characterized inthat, in the apparatus in Item 133, in the light flux from the firstlight source, the wave front aberration of the light flux whosenumerical aperture is not more than NA1 when the light flux passesthrough the objective lens, at the best image point through thetransparent substrate of the first optical information recording mediumis not more than 0.07 λrms, and in the light flux from the second lightsource, the wave front aberration of the light flux whose numericalaperture is not more than NAH2 when the light flux passes through theobjective lens, at the best image point through the transparentsubstrate of the second optical information recording medium is not morethan 0.07 λrms.

Further, the optical pickup apparatus in Item 138 is characterized inthat, in the apparatus in Item 134, in the light flux from the firstlight source, the wave front aberration of the light flux whosenumerical aperture is not more than NAH1 when the light flux passesthrough the objective lens, at the best image point through thetransparent substrate of the first optical information recording mediumis not more than 0.07 λrms, and in the light flux from the second lightsource, the wave front aberration of the light flux whose numericalaperture is not more than NA2 when the light flux passes through theobjective lens, at the best image point through the transparentsubstrate of the second optical information recording medium is not morethan 0.07 λrms.

Further, the optical pickup apparatus in Item 139 is characterized inthat, in the apparatus in Item 135, in the light flux from the firstlight source, the wave front aberration of the light flux whosenumerical aperture is not more than NA1 when the light flux passesthrough the objective lens, at the best image point through thetransparent substrate of the first optical information recording mediumis not more than 0.07 λrms, and in the light flux from the second lightsource, the wave front aberration of the light flux whose numericalaperture is not more than NAH2 when the light flux passes through theobjective lens, at the best image point through the transparentsubstrate of the second optical information recording medium is not morethan 0.07 λrms.

Further, the optical pickup apparatus in Item 140 is characterized inthat, in the apparatus in Item 136, in the light flux from the firstlight source, the wave front aberration of the light flux whosenumerical aperture is not more than NAH1 when the light flux passesthrough the objective lens, at the best image point through thetransparent substrate of the first optical information recording mediumis not more than 0.07 λrms, and in the light flux from the second lightsource, the wave front aberration of the light flux whose numericalaperture is not more than NA2 when the light flux passes through theobjective lens, at the best image point through the transparentsubstrate of the second optical information recording medium is not morethan 0.07 λrms.

Further, the optical pickup apparatus in Item 141 is characterized inthat, in the apparatus in any one Item of Items 122–140, at least onecollimator is included between the first light source and the objectivelens, and between the second light source and the objective lens, andthe light flux entering into the objective lens from the first lightsource and the light flux entering into the objective lens from thesecond light source are respectively parallel light.

Further, the optical pickup apparatus in Item 142 is characterized inthat, in the apparatus in Item 141, the paraxial focus position of theobjective lens for the light flux form the first light source and theparaxial focus position of the objective lens for the light flux fromthe second light source almost coincide with each other.

Further, the optical pickup apparatus in Item 143 is characterized inthat, in the apparatus in Items 129, 133 and 137, the second diffractionpattern is provided outside the diffraction pattern, and the seconddiffraction pattern is set such that +first ordered diffracted ray ofthe second diffraction pattern to the light flux from the first lightsource is converged onto the light converging position, and the lightflux from the second light source is not diffracted by the seconddiffraction pattern.

Further, the optical pickup apparatus in Item 144 is characterized inthat, in the apparatus in Items 130, 134 and 138, the second diffractionpattern is provided outside the diffraction pattern, and the seconddiffraction pattern is set such that the light flux from the first lightsource becomes mainly +first ordered diffracted ray in the seconddiffraction pattern, and the light flux from the second light source istransmitted through the second diffraction pattern and is converged ontothe light converging position.

Further, the optical pickup apparatus in Item 145 is characterized inthat, in the apparatus in Items 131, 135 and 139, the second diffractionpattern is provided outside the diffraction pattern, and the seconddiffraction pattern is set such that −first ordered diffracted ray inthe second diffraction pattern is converged onto the light convergingposition to the light flux from the first light source, and the lightflux from the second light source is not diffracted by the seconddiffraction pattern.

Further, the optical pickup apparatus in Item 146 is characterized inthat, in the apparatus in Items 132, 136 and 140, the second diffractionpattern is provided outside the diffraction pattern, and the seconddiffraction pattern is set such that the light flux from the first lightsource becomes mainly −first ordered diffracted ray in the seconddiffraction pattern, and the light flux from the second light source istransmitted through the second diffraction pattern and is converged ontothe light converging position.

Further, the optical pickup apparatus in Item 147 is characterized inthat, in the apparatus in Items 129, 133 and 137, the second diffractionpattern is provided outside the diffraction pattern, and the seconddiffraction pattern is set such that the transmitted light of the seconddiffraction pattern to the light flux from the first light source isconverged onto the light converging position, and the light flux fromthe second light source becomes mainly −first ordered diffracted ray inthe second diffraction pattern.

Further, the optical pickup apparatus in Item 148 is characterized inthat, in the apparatus in Items 130, 134 and 138, the second diffractionpattern is provided outside the diffraction pattern, and the seconddiffraction pattern is set such that the light flux from the first lightsource passes through the second diffraction pattern, and the light fluxfrom the second light source becomes mainly −first ordered diffractedray in the second diffraction pattern, and is converged onto the lightconverging position.

Further, the optical pickup apparatus in Item 149 is characterized inthat, in the apparatus in Items 131, 135 and 139, the second diffractionpattern is provided outside the diffraction pattern, and the seconddiffraction pattern is set such that the transmitted light of the seconddiffraction pattern to the light flux from the first light source isconverged onto the light converging position, and the light flux fromthe second light source becomes mainly +first ordered diffracted ray inthe second diffraction pattern.

Further, the optical pickup apparatus in Item 150 is characterized inthat, in the apparatus in Items 132, 136 and 140, the second diffractionpattern is provided outside the diffraction pattern, and the seconddiffraction pattern is set such that the light flux from the first lightsource passes through the second diffraction pattern, and the light fluxfrom the second light source becomes mainly +first ordered diffractedray in the second diffraction pattern, and is converged onto the lightconverging position.

Further, the optical pickup apparatus in Item 151 is characterized inthat, in the apparatus in Items 129, 131, 133, 135 137 or 139, theapparatus includes a light wave composing means by which the emittedlight flux from the first light source and the emitted light flux fromthe second light source can be composed, and has the opening limitingmeans which transmits the light flux from the first light source, and inthe light flux from the second light source, which does not transmit theflux which passes through the opposite side area to the optical axis ofthe diffraction pattern, between the light wave composing means and theoptical information recording medium.

Further, the optical pickup apparatus in Item 151 is characterized inthat, in the apparatus in Items 129, 131, 133, 135 137 or 139, theapparatus includes a light wave composing means by which the emittedlight flux from the first light source and the emitted light flux fromthe second light source can be composed, and has the opening limitingmeans which transmits the light flux from the second light source, andin the light flux from the first light source, which does not transmitthe flux which passes through the opposite side area to the optical axisof the diffraction pattern, between the light wave composing means andthe optical information recording medium.

Further, the optical pickup apparatus in Item 153 is characterized inthat, in the apparatus in Item 151, the opening limiting means is aannular band filter, which transmits the light flux from the first lightsource, and in the light flux of the second light source, which reflectsor absorbs the flux which passes through the opposite side area to theoptical axis of the diffraction pattern.

Further, the optical pickup apparatus in Item 154 is characterized inthat, in the apparatus in Item 152, the opening limiting means is aannular band filter, which transmits the light flux from the secondlight source, and in the light flux of the first light source, whichreflects or absorbs the flux which passes through the opposite side areato the optical axis of the diffraction pattern.

Further, the optical pickup apparatus in Item 155 is characterized inthat, in the apparatus in Item 151, the opening limiting means is aannular band filter, which transmits the light flux from the first lightsource, and in the light flux of the second light source, whichdiffracts the flux which passes through the opposite side area to theoptical axis of the diffraction pattern.

Further, the optical pickup apparatus in Item 156 is characterized inthat, in the apparatus in Item 152, the opening limiting means is aannular band filter, which transmits the light flux from the secondlight source, and in the light flux of the first light source, whichdiffracts the flux which passes through the opposite side area to theoptical axis of the diffraction pattern.

Further, the optical pickup apparatus in Item 157 is characterized inthat, in the apparatus in any one Item of Items 122–156, the lightdetector is in common to the first light source and the second lightsource.

Further, the optical pickup apparatus in Item 158 is characterized inthat, in the apparatus in any one Item of Items 122–156, the lightdetector is provided separately the first light detector for the firstlight source and the second light detector for the second light source,and these are spatially separated position respectively.

Further, the optical pickup apparatus in Item 159 is characterized inthat, in the apparatus in Item 158, at lest a pair of the first lightsource and the first light detector or the second light source and thesecond light detector, is formed into a unit.

Further, the optical pickup apparatus in Item 160 is characterized inthat, in the apparatus in Item 157, the first light source, the secondlight source, and a common light detector (a single light detector) areformed into a unit.

Further, the optical pickup apparatus in Item 161 is characterized inthat, in the apparatus in Item 158, in the light detector, the firstlight detector of the first light source and the second light detectorof the second light source are separately provided, and the first lightsource, the second light source, the first light detector and the secondlight source are formed into a unit.

Further, the optical pickup apparatus in Item 162 is characterized inthat, in the apparatus in any one Item of Items 122–161, further thelight detector to detect the transmitted light from the optical disk, isprovided.

Further, the optical pickup apparatus in Item 163 which has: the firstlight source with the wavelength λ1; the second light source with thewavelength λ2 (λ1≠λ2); the wave composing means by which the emittedlight flux from the first light source and the emitted light flux fromthe second light source can be composed; the diffraction optical elementhaving the diffraction pattern on at least one surface; the objectivelens by which the light flux from respective light sources are convergedonto the information recording surface of the optical informationrecording medium through the transparent substrate; and the lightdetector which receives the reflected light of the emitted light fluxfrom the first light source and the second light source, from theoptical information recording medium, the optical pickup apparatus ischaracterized in that the m-ordered diffracted ray (where, m is aninteger except 0) from the diffraction pattern of the objective lens ofthe light flux from the first light source is at least used, thereby,the first optical information recording medium in which the thickness ofthe transparent substrate is t1 is recorded and/or played back, and then-th ordered diffracted ray (where, n=m) from the diffraction pattern ofthe objective lens of the light flux from the second light source is atleast used, thereby, the second optical information recording medium inwhich the thickness of the transparent substrate is t2 (t2≠t1) isrecorded and/or played back.

Further, the optical pickup apparatus in Item 164 is characterized inthat, in the apparatus in Item 163, the optical pickup apparatus is usedunder the relationship that the wavelengths λ1 and λ2 of the first lightsource and the second light source are λ1<λ2, and the thickness t1 andt2 of the transparent substrates are t1<t2 and the m-ordered and n-thordered diffracted ray are both +first ordered diffracted ray.

Further, the optical pickup apparatus in Item 165 is characterized inthat, in the apparatus in Item 163, the optical pickup apparatus is usedunder the relationship that the wavelengths λ1 and λ2 of the first lightsource and the second light source are λ1<λ2, and the thickness t1 andt2 of the transparent substrates are t1>t2 and the m-ordered and n-thordered diffracted ray are both −first ordered diffracted ray.

Further, the optical pickup apparatus in Item 166 is characterized inthat, in the apparatus in Items 163, 164 and 165, the diffractionoptical element and the objective lens are integrally driven.

Further, the optical pickup apparatus in Item 167 is characterized inthat, in the apparatus in Items 122–166, the depth in the optical axisof the first diffraction pattern is not more than 2 μm.

Further, the objective lens for the optical pickup apparatus in Item 168is characterized in that it has the diffraction pattern on at least onesurface, and when the light flux of the wavelength λ1 enters, at leastm-ordered diffracted ray (where, m is an integer except 0) from thediffraction pattern is converged onto the first light convergingposition and when the light flux of the wavelength λ2 enters, at leastn-th ordered diffracted ray (where, n=m) from the diffraction pattern isconverged onto the second light converging position which is differentfrom the first light converging position.

Further, the objective lens for the optical pickup apparatus in Item 169is characterized in that, when the wavelengths λ1, λ2 are λ1<λ2, thefirst light converging position is the light converging position to thefirst optical information recording medium in which the thickness of thetransparent substrate is t1, the second light converging position is thelight converging position to the second optical information recordingmedium in which the thickness of the transparent substrate is t2 and thethickness t1, t2 of the transparent substrate are t1<t2 the m-orderedand n-th ordered diffracted ray are both +first ordered diffracted ray.

Further, the objective lens for the optical pickup apparatus in Item 170is characterized in that, when the wavelengths λ1, λ2 are λ1<λ2, thefirst light converging position is the light converging position to thefirst optical information recording medium in which the thickness of thetransparent substrate is t1, the second light converging position is thelight converging position to the second optical information recordingmedium in which the thickness of the transparent substrate is t2, andthe thickness t1, t2 of the transparent substrate are t1>t2 them-ordered and n-th ordered diffracted ray are both −first ordereddiffracted ray.

Further, the objective lens for the optical pickup apparatus in Item 171is characterized in that it has the diffraction pattern on at least onesurface, and when the light flux of the wavelength λ1 enters, at leastm-ordered diffracted ray (where, m is an integer except 0) from thediffraction pattern has the light converging position which is used forrecording and/or reproducing the first optical information recordingmedium in which the thickness of the transparent substrate is t1, andwhen the light flux of the wavelength λ2 (where, λ2≠λ1) enters, at leastn-th ordered diffracted ray (where, n=m) from the diffraction patternhas the light converging position which is used for recording and/orreproducing the second optical information recording medium in which thethickness of the transparent substrate is t2 (where, t2≠t1).

Further, the objective lens for the optical pickup apparatus in Item 172is characterized in that, in the objective lens in Item 171, when thewavelengths λ1, λ2 are λ1<λ2, and the thickness t1, t2 of thetransparent substrates are t1<t2 the m-ordered and n-th ordereddiffracted ray are both +first ordered diffracted ray.

Further, the objective lens for the optical pickup apparatus in Item 173is characterized in that, in the objective lens in Item 171, when thewavelengths λ1, λ2 are λ1<λ2, and the thickness t1, t2 of thetransparent substrates are t1>t2 the m-ordered and n-th ordereddiffracted ray are both −first ordered diffracted ray.

Further, the objective lens for the optical pickup apparatus in Item 174is characterized in that, in the objective lens in Item 172, when thenecessary numerical aperture on the optical information recording mediumside of the objective lens necessary for recording and/or reproducingthe first optical information recording medium in which the thickness ofthe transparent substrate is t1, by the first light source with thewavelength λ1, is NA1, and the necessary numerical aperture on theoptical information recording medium side of the objective lensnecessary for recording and/or reproducing the second opticalinformation recording medium in which the thickness of the transparentsubstrate is t2 (t2>t1), by the second light source with the wavelengthλ2 (λ2>λ1), is NA2 (NA2<NA1), the diffraction pattern provided on atleast one surface of the objective lens is the rotation symmetry to theoptical axis, and +first ordered diffracted ray from the circumferencemost separated from the optical axis of the diffraction pattern of theobjective lens of the light flux from the first light source isconverted into the light flux whose numerical aperture on the opticalinformation recording medium side is NAH1, and +first ordered diffractedray from the circumference nearest to the optical axis of thediffraction pattern of the objective lens of the light flux from thefirst light source is converted into the light flux whose numericalaperture on the optical information recording medium side is NAL1, andthe following conditions are satisfied: NAH1<NA1,0≦NAL1≦NA2.

Further, the objective lens for the optical pickup apparatus in Item 175is characterized in that, in the objective lens in Item 172, when thenecessary numerical aperture on the optical information recording mediumside of the objective lens necessary for recording and/or reproducingthe first optical information recording medium in which the thickness ofthe transparent substrate is t1, by the first light source with thewavelength λ1, is NA1, and the necessary numerical aperture on theoptical information recording medium side of the objective lensnecessary for recording and/or reproducing the second opticalinformation recording medium in which the thickness of the transparentsubstrate is t2 (t2>t1), by the second light source with the wavelengthλ2 (λ2>λ1), is NA2 (NA2>NA1), the diffraction pattern provided on atleast one surface of the objective lens is the rotation symmetry to theoptical axis, and +first ordered diffracted ray from the circumferencemost separated from the optical axis of the diffraction pattern of theobjective lens of the light flux from the first light source isconverted into the light flux whose numerical aperture on the opticalinformation recording medium side is NAH1, and +first ordered diffractedray from the circumference nearest to the optical axis of thediffraction pattern of the objective lens of the light flux from thefirst light source is converted into the light flux whose numericalaperture on the optical information recording medium side is NAL1, andthe following conditions are satisfied: NAH1<NA2,0≦NAL1≦NA1.

Further, the objective lens for the optical pickup apparatus in Item 176is characterized in that, in the objective lens in Item 173, when thenecessary numerical aperture on the optical information recording mediumside of the objective lens necessary for recording and/or reproducingthe first optical information recording medium in which the thickness ofthe transparent substrate is t1, by the first light source with thewavelength λ1, is NA1, and the necessary numerical aperture on theoptical information recording medium side of the objective lensnecessary for recording and/or reproducing the second opticalinformation recording medium in which the thickness of the transparentsubstrate is t2 (t2<t1), by the second light source with the wavelengthλ2 (λ2>λ1), is NA2 (NA2<NA1), the diffraction pattern provided on atleast one surface of the objective lens is the rotation symmetry to theoptical axis, and −first ordered diffracted ray from the circumferencemost separated from the optical axis of the diffraction pattern of theobjective lens of the light flux from the first light source isconverted into the light flux whose numerical aperture on the opticalinformation recording medium side is NAH1, and −first ordered diffractedray from the circumference nearest to the optical axis of thediffraction pattern of the objective lens of the light flux from thefirst light source is converted into the light flux whose numericalaperture on the optical information recording medium side is NAL1, andthe following conditions are satisfied:NAH1<NA1,0≦NAL1≦NA2.

Further, the objective lens for the optical pickup apparatus in Item 177is characterized in that, in the objective lens in Item 173, when thenecessary numerical aperture on the optical information recording mediumside of the objective lens necessary for recording and/or reproducingthe first optical information recording medium in which the thickness ofthe transparent substrate is t1, by the first light source with thewavelength λ1, is NA1, and the necessary numerical aperture on theoptical information recording medium side of the objective lensnecessary for recording and/or reproducing the second opticalinformation recording medium in which the thickness of the transparentsubstrate is t2 (t2<t1), by the second light source with the wavelengthλ2 (λ2>λ1), is NA2 (NA2>NA1), the diffraction pattern provided on atleast one surface of the objective lens is the rotation symmetry to theoptical axis, and −first ordered diffracted ray from the circumferencemost separated from the optical axis of the diffraction pattern of theobjective lens of the light flux from the first light source isconverted into the light flux whose numerical aperture on the opticalinformation recording medium side is NAH1, and −first ordered diffractedray from the circumference nearest to the optical axis of thediffraction pattern of the objective lens of the light flux from thefirst light source is converted into the light flux whose numericalaperture on the optical information recording medium side is NAL1, andthe following conditions are satisfied:NAH1<NA2,0≦NAL1≦NA1.

Further, the objective lens for the optical pickup apparatus in Item 178is characterized in that, in the objective lens in any one Item of Items168–177, the optical surface includes the diffraction pattern portionand the refraction portion, and the bordered between the diffractionportion and the refraction portion includes the difference in level notless than 5 μm.

Further, the objective lens for the optical pickup apparatus in Item 179is characterized in that, in the objective lens in any one Item of Items168–177, the average depth of the diffraction pattern of the diffractionportion nearest to the optical axis side is not more than 2 μm.

Further, the objective lens for the optical pickup apparatus in Item 180is characterized in that, in the objective lens in Item 179, the averagedepth of the diffraction pattern of the diffraction portion nearest tothe optical axis side is not more than 2 μm, and the average depth ofthe diffraction pattern of the diffraction portion most separated fromthe optical axis side is not less than 2 μm.

Further, the objective lens for the optical pickup apparatus in Item 181is characterized in that, in the objective lens in any one Item of Items168–180, the diffraction pattern of the optical surface includes theoptical axis portion.

Further, the objective lens for the optical pickup apparatus in Item 182is characterized in that, in the objective lens in any one Item of Items168–180, the optical axis portion of the optical surface is not providedwith the diffraction pattern, and is the refraction surface.

Further, the objective lens for the optical pickup apparatus in Item 183is characterized in that, in the objective lens in Items 168, 169, 171,172 or 174, when an image is formed on the information recording surfaceat a predetermined image forming magnification through the transparentsubstrate of the thickness 0.6 mm at the wavelength of the light sourceof 650 nm, it has the diffraction limit performance up to at leastnumerical aperture 0.6, and when an image is formed on the informationrecording surface at a predetermined image forming magnification throughthe transparent substrate of the thickness 1.2 mm at the wavelength ofthe light source of 780 nm, it has the diffraction limit performance upto at least numerical aperture 0.45.

Further, the objective lens for the optical pickup apparatus in Item 184is characterized in that, in the objective lens in Item 183, the numberof steps of the diffraction pattern is not more than 15.

Further, the objective lens for the optical pickup apparatus in Item 185is characterized in that, in the objective lens in any one Item of Items168–184, the optical surface on which the diffraction pattern isprovided is a convex surface.

Further, the objective lens for the optical pickup apparatus in Item 186is characterized in that, in the objective lens in Item 185, therefraction portion of the optical surface on which the diffractionpattern is provided, is aspherical.

Further, the objective lens for the optical pickup apparatus in Item 187is characterized in that, in the objective lens in Item 186, thediffraction pattern includes at least one aspherical refraction portion.

Further, the objective lens for the optical pickup apparatus in Item 188is characterized in that, in the objective lens in any one Item of Items168–187, the objective lens is a single lens.

Further, the objective lens for the optical pickup apparatus in Item 189is characterized in that, in the objective lens in Item 188, thediffraction pattern is provided on only one optical surface of thesingle lens.

Further, the objective lens for the optical pickup apparatus in Item 185is characterized in that, in the objective lens in Item 188, thediffraction pattern is provided on only one optical surface of thesingle lens, and the other optical surface is aspherical.

No-aberration parallel light is entered from the first light source intosuch that objective lens, and by using an exclusive use objective lenswhich is designed such that the parallel light is converged withno-aberration through the transparent substrate (the thickness is t1) ofthe first optical information recording medium, the case where theparallel light with no-aberration enters from the second light source tothis objective lens and passes through the transparent substrate(thickness t2, t2>t1) of the second optical information recordingmedium, will be considered as follows.

To the entered parallel light, when there is no substrate and thewavelength is λ1, the back focus is fB1, and when the wavelength is λ2(λ2>λ1), the back focus is fB2.

In this case, the axial chromatic aberration ΔfB is defined asΔfB=fB2−fB1  (1),when the objective lens is a refraction type aspherical single lens,ΔfB>0.

Further, when the wavelength is λ2 and the light is converged throughthe transparent substrate of the second optical information recordingmedium, the spherical aberration when the axial focus position is madeto be the reference, does not become 0 due to the following factors:

-   (1) The spherical aberration due to the wavelength dependency of the    refractive index of the objective lens by the change of the    wavelength from λ1 to λ2.-   (2) The spherical aberration generated by the difference between the    thickness t1 of the transparent substrate of the first optical    information recording medium and the thickness t2 of the transparent    substrate of the second optical information recording medium.-   (3) The spherical aberration due to the difference between the    refractive index nd1 (λ1) of the transparent substrate of the first    optical information recording medium and the refractive index nd2    (λ2) of the transparent substrate of the second optical information    recording medium.

When the objective lens is the refraction type aspherical single lens,the spherical aberration due to factor (1) becomes over. The sphericalaberration due to factor (2) becomes also over. Further, nd2<nd1, andthe spherical aberration due to factor (3) becomes also over.

In the over-spherical aberration which is generated due to factors(1)–(3), the spherical aberration due to factor (2) is almost all, andthat due to factor (1) is next to it. The spherical aberration due tofactor (3) can be almost neglected.

The above-described presupposition corresponds to the case in which, forexample, the first optical information recording medium is the DVD, thewavelength λ1 of the first light source is 650 nm, and the secondoptical information recording medium is the CD, the wavelength λ2 of thesecond light source is 780 nm, and in the DVD (thickness t1=0.6 mm) andthe CD (thickness t2=1.2 mm), the material of the transparent substrateis the same, but the thickness is different.

Next, when the +first ordered diffracted ray of the diffraction patternwhich is the rotation symmetry to the optical axis is viewed, as shownin FIG. 113( a), when the wavelength is longer, the diffraction angle ofthe +first ordered light is larger, and the +first ordered light is morediffracted to the optical axis side, and is bent to more under side.That is, when the parallel light flux with no-aberration enters from thesecond light source with the wavelength λ2, the +first ordered light hasan action to make the axial chromatic aberration and the sphericalaberration under, as compared to the case where the parallel light fluxwith no-aberration enters from the first light source with thewavelength λ1. By using this action, the difference between thespherical aberration when the light is through the transparent substrateof the second optical information recording medium with the wavelengthλ2 and the spherical aberration when the light is through thetransparent substrate of the first optical information recording mediumwith the wavelength λ1, can be reduced by introducing the diffractionpattern of the rotation symmetry and using the +first ordered diffractedray.

When the thickness t1 of the substrate of the first optical informationrecording medium is larger than the thickness t2 of the transparentsubstrate of the second optical information recording medium, thespherical aberration due to the factor (2) becomes under, and as shownin FIG. 12( b), by using the −first ordered diffracted ray having theaction by which the axial chromatic aberration and the sphericalaberration to be generated, become over, the aberration can be reduced.

In the present invention, in the case where the +first ordereddiffracted ray is used, when the refractive index of the material of theobjective lens at the wavelength λ1 is n(λ1), and the refractive indexof the material of the objective lens at the wavelength λ2 is n(λ2), thedepth of the diffraction pattern is λ1/{n(λ1)−1} or λ2/{n(λ2)−1}, andeven if the plastic material with comparatively small refractive indexis used, the depth is not more than 2 μm, therefore, the production ofthe objective lens to which the diffraction pattern is integrated, iseasier than the conventional hologram optical element, or the hologramtype ring lens.

Further, the optical pickup apparatus in Item 191, which has: the firstlight source with the wavelength λ1; the second light source with thewavelength λ2 (λ1≠λ2); the objective lens having the diffraction patternon at least one surface, and converging the light flux from respectivelight sources onto the information recording surface of the opticalinformation recording medium through the transparent substrate; and thelight detector receiving the reflected light from the opticalinformation recording medium of the emitted light flux from the firstlight source and the second light source, the optical pickup apparatusis characterized in that, by using at least m-ordered diffracted ray(where, m is an integer except 0) from the diffraction pattern of theobjective lens of the light flux from the first light source, theoptical pickup apparatus conducts at least either one of recording andreproducing of the information to the first optical informationrecording medium in which the thickness of the transparent substrate ist1, and

by using at least n-th ordered diffracted ray (where, n=m) from thediffraction pattern of the objective lens of the light flux from thesecond light source, the optical pickup apparatus conducts at leasteither one of recording and reproducing of the information to the secondoptical information recording medium in which the thickness of thetransparent substrate is t2 (t2≠t1), the objective lens is made ofplastic material, the plastic material satisfies the relationship of thefollowing: when the temperature changes by ΔT (° C.), the changed amountof refractive index is defined as Δn, then,

−0.0002/° C.<Δn/ΔT<−0.00005/° C., and the first light source satisfiesthe following: when the temperature changes by ΔT (° C.), the changedamount of the emission wavelength is defined as Δλ1 (nm), then, 0.05nm/° C.<Δλ1/λT<0.5 nm/° C.

According to Item 191, the characteristic variation of the opticalpickup apparatus due to the temperature change of the refractive indexin the objective lens of plastic and the characteristic variation of theoptical pickup apparatus due to the temperature change of the wavelengthin the light source are acted toward the direction to be cancelled witheach other, and the compensation effect can be obtained, thereby, thepick-up apparatus which is very strong to the temperature change, can beobtained.

Further, the optical pickup apparatus in Item 192 which is providedwith: the first light source with the wavelength λ1; the second lightsource with the wavelength λ2 (λ1≠λ2); the objective lens having thediffraction pattern on at least one surface, and converging the lightflux from respective light sources onto the information recordingsurface of the optical information recording medium through thetransparent substrate; and the light detector receiving the reflectedlight from the optical information recording medium of the emitted lightflux from the first light source and the second light source, theoptical pickup apparatus is characterized in that, by using at leastm-ordered diffracted ray (where, m is an integer except 0) from thediffraction pattern of the objective lens of the light flux from thefirst light source, the optical pickup apparatus conducts at leasteither one of recording and reproducing of the information to the firstoptical information recording medium in which the thickness of thetransparent substrate is t1, and by using at least n-th ordereddiffracted ray (where, n=m) from the diffraction pattern of theobjective lens of the light flux from the second light source, theoptical pickup apparatus conducts at least either one of recording andreproducing of the information to the second optical informationrecording medium in which the thickness of the transparent substrate ist2 (t2≠t1), and the wavelengths λ1, λ2, and the thickness of thetransparent substrates t1 and t2 have the relationship λ2>λ1, t2>t1, andin the case where the necessary numerical aperture on the opticalinformation recording medium side of the objective lens necessary forrecording and/or reproducing the first optical information recordingmedium by the first light source is NA1, the focal distance of theobjective lens at the wavelength λ1 (mm) is f1 (mm), and theenvironmental temperature change is ΔT(° C.), when the changed amount ofthe third-ordered spherical aberration component of the wave frontaberration of the light flux converged onto the information recordingsurface of the first information recording medium is ΔWSA3 (λ1 rms), thefollowing relationship is satisfied:0.2×10⁻⁶/° C.<ΔWSA3·λ1/{f·(NA1)⁴ ·ΔT}<2.2×10⁻⁶ /° C.

According to Item 192, when the value of the objective term is not morethan the upper limit, even if the environmental temperature changes, thecharacteristic as the pick-up apparatus can be easily maintained, andwhen the value of the objective term is not less than the lower limit,even when only the wavelength changes, the characteristic as the pick-upapparatus can be easily maintained.

Further, the optical pickup apparatus in Item 193 is characterized inthat, in Items 191 or 192, at least one collimator is included betweenthe first light source and the objective lens, and the second lightsource and the objective lens, and the light flux entering from thefirst light source to the objective lens and the light flux enteringfrom the second light source to the objective lens, are respectivelyalmost parallel light.

Further, the optical pickup apparatus in Item 194 is characterized inthat, in Items 191, 192 or 193, t1 is 0.55 mm–0.65 mm, t2 is 1.1 mm–1.3mm, λ1 is 630 nm–670 nm, and λ2 is 760 nm–820 nm.

Further, the optical pickup apparatus in Item 192 which is providedwith: the first light source with the wavelength λ1; the second lightsource with the wavelength λ2 (λ1≠λ2); the objective lens having thediffraction pattern on at least one surface, and converging the lightflux from respective light sources onto the information recordingsurface of the optical information recording medium through thetransparent substrate; and the light detector receiving the reflectedlight from the optical information recording medium of the emitted lightflux from the first light source and the second light source, theoptical pickup apparatus is characterized in that, by using at leastm-ordered diffracted ray (where, m is an integer except 0) from thediffraction pattern of the objective lens of the light flux from thefirst light source, the optical pickup apparatus conducts at leasteither one of recording or reproducing of the information to the firstoptical information recording medium in which the thickness of thetransparent substrate is t1 , and by using at least n-th ordereddiffracted ray (where, n=m) from the diffraction pattern of theobjective lens of the light flux from the second light source, theoptical pickup apparatus conducts at least either one of recording orreproducing of the information to the second optical informationrecording medium in which the thickness of the transparent substrate ist2 (t2≠t1 ), and has a correction means for compensating the divergencedegree of the light flux entering from at least one light source of thefirst and the second light sources into the objective lens.

According to Item 195, by compensating the divergence degree of thelight flux entering into the objective lens, the third-ordered sphericalaberration of the whole optical system including the objective lens canbe corrected according to the design value.

Further, the optical pickup apparatus in Item 196 which, in Item 195,includes at least a collimator between the first light source and theobjective lens, and the second light source and the objective lens, andthe optical pickup apparatus in Item 197 is characterized in that thecorrection of the divergence degree by the correction means is conductedby changing the distance between the first and/or the second lightsource and at least one collimator. The correction of the divergencedegree by the correction means is characterized in that it is conductedby changing the distance between the first and/or the second lightsource and at least one collimator. By changing the distance between thelight source and the collimator, the divergence degree of the light fluxentering from at least one light source into the objective lens can becorrected.

Further, the optical pickup apparatus in Item 192 which is providedwith: the first light source with the wavelength λ1; the second lightsource with the wavelength λ2 (λ1≠λ2); the objective lens having thediffraction pattern on at least one surface, and converging the lightflux from respective light sources onto the information recordingsurface of the optical information recording medium through thetransparent substrate; and the light detector receiving the reflectedlight from the optical information recording medium of the emitted lightflux from the first light source and the second light source, theoptical pickup apparatus is characterized in that, by using at leastm-ordered diffracted ray (where, m is an integer except 0) from thediffraction pattern of the objective lens of the light flux from thefirst light source, the optical pickup apparatus conducts at leasteither one of recording or reproducing of the information to the firstoptical information recording medium in which the thickness of thetransparent substrate is t1 , and by using at least n-th ordereddiffracted ray (where, n=m) from the diffraction pattern of theobjective lens of the light flux from the second light source, theoptical pickup apparatus conducts at least either one of recording orreproducing of the information to the second optical informationrecording medium in which the thickness of the transparent substrate ist2 (t2≠t1 ), and the wave front aberration on the image formationsurface is not more than 0.07 λrms in the maximum numerical aperture onthe image side of the objective lens, to each of the light having 2different wavelengths (λ) outputted from the first and the second lightsources.

According to Item 198, there is no flare on each information recordingsurface and the light detector in recording and/or reproducing of thefirst and the second information recording medium, thereby, thecharacteristic of the optical pickup apparatus becomes excellent.

Further, the optical pickup apparatus in Item 199 is characterized inthat, in any one Item of Items 122–156, and 198, the first light sourceand the second light source are formed into a unit, and the lightdetector is in common to the first light source and the second lightsource.

Hereinafter, referring to the drawings, detailed embodiments of thepresent invention will be described.

An optical system of the first embodiment of the present invention isbasically a 2-sided aspherical single lens, and diffraction annularbands (ring zonal diffraction surface) are provided on one asphericalsurface. Generally, in the aspherical refractive surface, when thespherical aberration is corrected to a certain dominant wavelengthlight, to the wavelength light whose wavelength is shorter than that ofthe dominant wavelength light, the spherical aberration becomes under(insufficient correction). Reversely, in a diffraction lens which is alens having the diffraction surface, when the spherical aberration iscorrected by the dominant wavelength light, the spherical aberration canbe over (excessive correction) at the wavelength which is shorter thanthat of the dominant wavelength light. Accordingly, when an asphericalcoefficient of the aspherical surface lens by the refraction, and ancoefficient of the phase difference function of the diffraction lens areproperly selected and the refraction power and diffraction power arecombined, the spherical aberration can be finely corrected by both of 2different wavelength light.

Further, generally, the pitch of the diffraction annular band is definedby using the phase difference function or the optical path differencefunction, which will be detailed in a later example. Concretely, thephase difference function ΦB is expressed in the following [Equation 1]in radian unit, and the optical path difference function Φb is expressedby [Equation 2] in mm unit.

$\begin{matrix}{\Phi_{B} = {\sum\limits_{i - 1}^{\infty}\;{B_{2\; i}h_{21}}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack \\{\Phi_{b} = {\sum\limits_{i = 1}^{\infty}\;{b_{2\; i}h_{2i}}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

These 2 expression methods are, although the unit is different from eachother, equal to each other in a meaning that these express the pitch ofthe diffraction annular band. That is, to the dominant wavelength λ (mmunit), when the coefficient B of the phase difference function ismultiplied by λ/2π, it can be converted into the coefficient b of theoptical path difference function, or reversely, when the coefficient bof the optical path difference function is multiplied by 2π/λ, it can beconverted into the coefficient B of the phase difference function.

Herein, for a simple explanation, the diffraction lens which uses firstordered diffracted ray, will be described. In the case of the opticalpath difference function, the annular band is notched for each time whenthe function value exceeds the integer times of the dominant wavelengthλ, and in the case of the phase difference function, the annular band isnotched for each time when the function value exceeds the integer timesof 2π.

For example, a lens in which the diffraction annular band is notched onthe side of 2-sided cylindrical material having no refraction power, isconsidered, and when the dominant wavelength is 0.5 μm=0.0005 mm, thesecond power coefficient (second power term) of the optical pathdifference function is −0.05 (when converted into the second powercoefficient of the phase difference function, it is −628.3), and otherpower coefficients are all zero, the diameter of the first annular bandis h=0.1 mm, and the diameter of the second annular band is h=0.141 mm.Further, as for the focal distance f of this diffraction lens, to secondpower coefficient b2 of the optical path difference function b2=−0.05,f=−1/(2·b2)=10 mm is known.

Herein, in the case where the above definition is used as the base, whenthe second power coefficient of the phase difference function or theoptical path difference function is a value of not zero, the chromaticaberration near the optical axis, so-called in the paraxial area, can becorrected. Further, when coefficients other than the second powercoefficient of the phase difference function or the optical pathdifference function, for example, fourth power coefficient, sixth powercoefficient, eighth power coefficient, tenth power coefficients, etc.,are made to a value of not zero, the spherical aberration between 2wavelengths can be controlled. Incidentally, herein, “control” meansthat the difference of spherical aberration between 2 wavelengths can bemade very small, and the difference which is necessary for the opticalspecification can also be provided.

As the concrete application of the above description, when collimatelight (parallel light) from 2 light sources having different wavelengthsare made to simultaneously enter into the objective lens, and toimage-form on the optical disk, it is preferable that, initially, theparaxial axial chromatic aberration is corrected by using the secondpower coefficient of the phase difference function or the optical pathdifference function, and further, the difference between 2 wavelengthsof the spherical aberration is made smaller so that it is within theallowable value, by using the coefficients of the fourth power andsubsequent powers of the phase difference function or the optical pathdifference function.

Further, as another example, the specification in which one objectivelens is used for the light from 2 light sources having differentwavelengths, and for the light of one wavelength, the aberration iscorrected for the disk having the thickness (the thickness of thetransparent substrate) of t1, and for the light of the other wavelength,the aberration is corrected for the disk having the thickness of t2,will be considered below. In this case, when the coefficients subsequentto fourth power of the phase difference function or the optical pathdifference function are mainly used, the difference of the sphericalaberration between 2 wavelengths is provided, and the sphericalaberration can be made to be corrected by respective wavelengths forrespective thickness. Further, in both cases, for the refractionsurface, the aspherical surface is better than the spherical surface foreasy aberration correction between 2 wavelengths.

The above-described aspherical refraction surface has respectivedifferent refraction powers for different wavelengths, and has differentlight converging points, therefore, respective light converging pointscan correspond to optical disks having respective substrate thickness.In this case, the shorter wavelength of the light source is not morethan 700 nm, the longer wavelength of the light source is not less than600 nm, and it is preferable that the difference of the wavelengths isnot less then 80 nm. Further, it is more preferable that the differenceof the wavelengths is not more than 400 nm, and further preferably, thedifference of the wavelengths is not less than 100 nm, and not more than200 nm. It is desirable that the diffraction surface has, to the lighthaving 2 different wavelengths, the maximum diffraction efficiency atalmost the middle wavelength thereof, however, the diffraction surfacemay have the maximum diffraction efficiency at either one wavelength.

By using the same action as the correction of the spherical aberration,the diffraction annular band lens is provided on the optical surface,and for each of the light sources with 2 different wavelengths, theaxial chromatic aberration can be corrected by a certain one sameordereded diffracted ray. That is, the axial chromatic aberration forthe light of the light sources with 2 different wavelengths can becorrected within the range of ±λ/(2NA2). Where, λ is the longerwavelength of 2 wavelengths, and NA is an image side numerical aperturecorresponding to the longer wavelength.

Further, when the difference of wavelengths of the light sources with 2different wavelengths is not less than 80 nm, and Abbe's number of theglass material of the objective lens is νd, the following conditionalexpressionνd>50  (1)is desirably satisfied. The conditional expression (1) is a condition toreduce the second ordered spectrum when the axial chromatic aberrationis corrected for the light sources with 2 different wavelengths.

Next, when the diffraction surface is provided on one surface of a thinsingle lens, the whole single lens is considered as the composition ofthe refraction lens as a base from which the diffraction relief is takenoff and the diffraction surface, and the chromatic aberration of thiscomposition lens will be considered below. The achromatic condition by acertain wavelength λx and the wavelength λy (λx<λy) is as follow.fR·νR+fD·νD=0Where, fR, fD: a focal distance of respective refraction lens anddiffraction surface, and νR, νD: Abbe's number of respective refractionlens and diffraction surface, and are determined by the followingexpressions:νR=(n0−1)/(nx−ny)νD=λ0/(λx−λy)

Where, n0: the refractive index at the reference wavelength, and λ0: thereference wavelength.

In this case, the chromatic aberration δf to a certain wavelength λz isexpressed by the following equation:δf=f(θR−θD)/(νR−νD)  (2)Where, θR, θD: respective partial variance ratios of the refraction lensand the diffraction surface, and are determined by the followingequations.θR=(nx−nz)/(nx−ny)θD=(λx−λz)/(λx−λy)where, nz: the refractive index at the wavelength λz.

As an example, when λ0=λx=635 nm, λy=780 nm, λz=650 nm, and the glassmaterial of the refraction lens as the base is BSC7 (νd=64.2) made byHoya Co., then, νR=134.5, νD=−4.38, θR=0.128, θD=0.103, are obtained,and then, δf=0.18×10⁻³f is obtained.

Further, when the glass material of the refraction lens as the base ischanged to E-FD1 (νd=29.5) made by Hoya Co., then, νR=70.5, θR=0.136 areobtained, and then, δf=0.44×10⁻³f is obtained.

As described above, in Equation (2), in the denominator of the rightside (νR−νD), because |νD| is very smaller than |νR|, the change ofAbbe's number νR of the refraction lens is dominant over the change ofthe chromatic aberration δf by replacing the glass material of therefraction lens. On the one hand, θR and θD are determined only by thewavelength, and the contribution of the change of the numerator (θR−θD)of the right side is smaller than that of the denominator (νR−νD) of theright side.

According to the above description, in the lens having the diffractionsurface, in ordered to suppress the secondary spectrum δf small, it isunderstood that the selection of the material having the larger Abbe'snumber νR is effective for the material of the refraction lens. Theconditional expression (1) shows the effective limit to suppress thesecondary spectrum so as to cope with the change of wavelength of thelight source.

Further, in the case where the achromatic processing is conductedwithout using the diffraction surface and by adhering the refractionlenses of 2 kinds of materials, when, for respective materials,θR=a+b·νR+ΔθR (a, b are constant) is expressed, if ΔθR is small, andthere is no abnormal dispersibility, the secondary spectrum δf does notdepend on Abbe's number νR of 2 refraction lenses. Accordingly, it isunderstood that the expression (1) is a condition specific to thediffraction optical system.

In ordered to easily produce the diffractive lens in the presentembodiment, it is preferable that the objective lens is composed ofplastic material. AS the plastic material to satisfy the conditionalexpression (1), acrylic system, polyolefine system plastic materials areused, however, from the view point of humidity resistance and heatresistance, the polyolefine system is preferable.

Next, the objective lens of the second embodiment of the presentinvention and the structure of the optical pickup apparatus providedwith the objective lens will be concretely described.

In FIG. 48, the schematic structural view of the optical pickupapparatus of the present embodiment will be shown. The optical disks 20which are optical information recording media onto which or from whichthe information is recorded and/or played back by the optical pickupapparatus, are 3 types of disks which are the first optical disk (forexample, a DVD) whose transparent substrate thickness is t1 and thesecond optical disk (for example, a blue laser use next-generation highdensity optical disk), and the third optical disk (for example, a CD)whose transparent substrate thickness is t2 different from t1, andhereinafter, these disks will be described as optical disks 20. Herein,the transparent substrate thickness t1=0.6 mm, and t2=1.2 mm.

The optical pickup apparatus shown in the drawing has, as the lightsources, the first semiconductor laser 11 (wavelength λ₁=610 nm–670 nm)which is the first light source, the blue laser 12 (wavelength λ₂=400nm–440 nm) which is the second light source, and the secondsemiconductor laser 13 (wavelength λ₃=740 nm–870 nm) which is the thirdlight source, and has the objective lens 1 as a part of the opticalsystem. The first light source, second light source and third lightsource are selectively used corresponding to the optical disks to recordand/or reproduce the information.

The diverging light flux emitted from the first semiconductor laser 11,the blue laser 12 or the second semiconductor laser 13 transmits throughthe transparent substrate 21 of the optical disk 20 through the beamsplitter 19 and the diaphragm 3, and is converged onto respectiveinformation recording surfaces 22 by the objective lens 1, and formsspots.

The incident light from each laser becomes modulated reflected light bythe information pit on the information recording surface 22, and entersinto the common light detector 30 through the beam splitter 18 and atoric lens 29, and by using its output signal, the read-out signal ofthe information recorded on the optical disk 20, the focusing detectionsignal and the track detection signal are obtained.

Further, the diaphragm 3 provided in the optical path is, in thisexample, a diaphragm having the fixed numeral aperture (NA 0.65), andsuperfluous mechanism is not needed, therefore, cost reduction can berealized. Incidentally, when the third disk is recorded and/or playedback, the numeral aperture of the diaphragm 3 may be changeable so thatthe unnecessary light (more than NA 0.45) can be removed.

When the zonal filter is integrally formed on the optical surface of theobjective lens 1 so that the light flux of a part of the outside of thepractically used aperture is shielded, the flare light of the outside ofthe practically used aperture can also be easily removed by the low coststructure.

When a definite conjugation type optical system is used as in thepresent embodiment, it is necessary that the relationship between thelight source and light converging optical system is kept constant tomaintain the light converging performance, and it is desirable that asthe movement for focusing or tracking, the light sources 11, 12 and 13and the objective lens 1 are moved as one unit.

Next, the objective lens and the structure of the optical pickupapparatus including the objective lens of the third embodiment of thepresent invention, will be concretely described.

In FIG. 49, the schematic structural view of the optical pickupapparatus of the present embodiment will be shown. The optical pickupapparatus shown in FIG. 49 is an example in which the laser/detectorintegration unit 40 into which the laser, light detector, and hologramare structured as a unit, is used, and the same components as in FIG. 48are shown by the same numeral codes. In this optical pickup apparatus,the first semiconductor laser 11, blue laser 12, the first lightdetection means 31, the second light detection means 32 and the hologrambeam splitter 23 are structured into a unit as the laser/detectorintegration unit 40.

When the first optical disk is played back, the light flux emitted fromthe first semiconductor laser 11 transmits trough the hologram beamsplitter 23, and is stopped down by the diaphragm 3, and converged ontothe information recording surface 22 by the objective lens 1 through thetransparent substrate 21 of the first optical disk 20. Then, the lightflux modulated by the information pit and reflected on the informationrecording surface 22 is diffracted again on the surface of the disk sideof the hologram beam splitter 23 through the objective lens 1 and thediaphragm 3, and enters onto the first light detector 31 correspondingto the first semiconductor laser 11. Then, by using the output signal ofthe first light detector 31, the read-out signal of the informationrecorded on the first optical disk 20, focusing detection signal, andtrack detection signal are obtained.

When the second optical disk is played back, the light flux emitted fromthe blue laser 12 is diffracted by the surface on the laser side of thehologram beam splitter 23, and advances on the same optical path as thelight flux from the first semiconductor laser 11. That is, the surfaceon the semiconductor laser side of the hologram beam splitter 23functions as the light composition means. Further, this light flux isconverged onto the information recording surface 22 through thediaphragm 3, objective lens 1, and through the transparent substrate 21of the second optical disk 20. Then, the light flux modulated by theinformation pit and reflected on the information recording surface 22,is diffracted by the surface on the disk side of the hologram beamsplitter 23 through the objective lens 1 and the diaphragm 3, and entersonto the second light detector 32 corresponding to the blue laser 12.Then, by using the output signal of the second light detector 32, theread-out signal of the information recorded on the second optical disk20, focusing detection signal, and track detection signal are obtained.

Further, when the third optical disk is played back, the laser/detectorintegration unit 41, which is structured into a unit by the secondsemiconductor laser 13, the third light detecting means 33, and thehologram beam splitter 24, is used. The light flux emitted from thesecond semiconductor laser 13 transmits through the hologram beamsplitter 24, and is reflected by the beam splitter 19 which is thecomposition means of the emitted light, stopped down by the diaphragm 3,and converged onto the information recording surface 22 through thetransparent substrate 21 of the optical disk 20 by the objective lens 1.Then, the light flux modulated by the information pit and reflected onthe information recording surface 22 is diffracted by the hologram beamsplitter 24 again through the objective lens 1, the diaphragm 3, and thebeam splitter 19, and entered onto the light detector 33. Then, by usingthe output signal of the third light detector 33, the read-out signal ofthe information recorded on the third optical disk 20, focusingdetection signal, and track detection signal are obtained.

In the optical pickup apparatus in the second and third embodiments, thezonal diffraction surface concentric with the optical axis 4 isstructured on the aspherical refraction surface of the objective lens 1.Generally, in the case where the objective lens is structured only bythe aspherical refraction surface, when the spherical aberration iscorrected for a certain wavelength λa, the spherical aberration becomesunder for the wavelength λb shorter than λa. On the one hand, in thecase where the diffraction surface is used, when the sphericalaberration is corrected for a certain wavelength λa, the sphericalaberration becomes over for the wavelength λb shorter than λa.Accordingly, when the aspherical surface optical design by therefraction surface, and the coefficient of the phase difference functionof the diffraction surface is appropriately selected, and the refractionpower and the diffraction power are combined, the spherical aberrationbetween different wavelengths can be corrected. Further, on theaspherical refraction surface, when the wavelength is different, therefraction power also changes, and the light converging position is alsodifferent. Accordingly, when the aspherical refraction surface isappropriately designed, the light with the different wavelength can alsobe converged onto the information recording surface 22 of eachtransparent substrate 21.

Further, in the objective lens 1 of the second and third embodiments,when the phase difference function of the aspherical refraction surfaceand the ring zonal diffraction surface is appropriately designed, thespherical aberration generated by the difference of the thickness of thetransparent substrates 21 of the optical disks 20 is corrected for eachlight flux emitted from the first semiconductor laser 11, blue laser 12,or the second semiconductor laser 13. Further, on the ring zonaldiffraction surface, when the coefficients of 4th power and subsequentterms of the power series are used as the phase difference functionexpressing the position of the annular band, the chromatic aberration ofthe spherical aberration can be corrected. Incidentally, as for thethird optical disk (CD), the aperture in the practical use is NA 0.45,and on the third optical disk, the spherical aberration is correctedwithin NA 0.45, and the spherical aberration in the outside area of NA0.45 is made the flare. By these corrections, for each optical disk 20,the aberration of the light converging spot on the image recordingsurface 22 becomes almost the same degree as the diffraction limit (0.07λrms) or lower than it.

Above-described optical pickup apparatus in the second and thirdembodiments can be mounted in a recording apparatus for the audio and/orimage, or a reproducing apparatus for the audio and/or image of acompatible player or drive, or an AV device in which these areassembled, personal computer, and other information terminals, forarbitrary different 2 or more of, that is, for a plurality of opticalinformation recording media, such as, for example, a CD, CD-R, CD-RW,CD-Video, CD-ROM, DVD, DVD-ROM, DVD-RAM, DVD-R, DVD-RW, MD, etc.

Next, the structure of the objective lens and the optical pickupapparatus including it of the fourth embodiment of the present inventionwill be concretely described.

FIG. 67 is a schematic structural view of the optical pickup apparatus10 of the present embodiment. In FIG. 67, the common members to those inthe second and the third embodiments are sometimes denoted by the samenumeral code. In FIG. 67, the optical pickup apparatus 10 records/playsback a plurality of optical disks 20 which are optical informationrecording media. Hereinafter, the plurality of optical disks 20 will bedescribed as the first optical disk (DVD) whose transparent substratethickness is t1, and the second optical disk (blue laser usenext-generation high density optical disk), and the third optical disk(CD) having the thickness t2 of the transparent substrate, which isdifferent from t1 . Herein, the thickness of the transparent substratet1=0.6 mm, t2=1.2 mm.

The optical pickup apparatus 10 has, as the light source, the firstsemiconductor laser 11 (the wavelength λ₁=610 nm–670 nm) which is thefirst light source, the blue laser 12 (the wavelength λ₂=400 nm–440 nm)which is the second light source, and the second semiconductor laser 13(the wavelength λ₁=740 nm–870 nm) which is the third light source. Thesefirst light source, second light source, and third light source areexclusively used corresponding to the optical disk to be recorded/playedback.

The light converging optical system 5 is a means for converging thelight flux emitted from the first semiconductor laser 11, blue laser 12and second semiconductor laser 13 onto the information recording surface22 through the transparent substrate 21 of the optical disk 20 and forforming the spot. In the present example, the light converging opticalsystem 5 has the collimator lens 2 to convert the light flux emittedfrom the light source into the parallel light (may be almost parallel),and the objective lens 1 to converge the light flux converted to theparallel light by the collimator lens 2.

On both surfaces of the objective lens 1, the ring zonal diffractionsurfaces which are concentric with the optical axis 4, are structured.Generally, in the case where the light converging optical system 5 isstructured by only the aspherical refraction surface, when the sphericalaberration is corrected for a certain wavelength λa, the sphericalaberration becomes under for the wavelength λb shorter than λa. On theone hand, in the case where the refraction surface is used, when thespherical aberration is corrected for a certain wavelength λa, thespherical aberration becomes over for the wavelength λb shorter than λa.Accordingly, when the aspherical surface optical design by therefraction surface, and the coefficient of the phase difference functionof the diffraction surface is appropriately selected, and the refractionpower and the diffraction power are combined, the spherical aberrationbetween different wavelengths can be corrected. Further, on theaspherical refraction surface, when the wavelength is different, therefraction power also changes, and the light converging position is alsodifferent. Accordingly, when the aspherical refraction surface isappropriately designed, the light with the different wavelength can alsobe converged onto the information recording surface 22 of eachtransparent substrate 21.

On the above-described ring zonal diffraction surface, the aberration iscorrected by using the first ordered diffracted ray for each light fluxemitted from the first semiconductor laser 11, the blue laser 12 or thesecond semiconductor laser 13. When the same ordered diffracted raycorresponds to the light flux, the loss of the light amount is smallerthan the case where the different ordered diffracted ray corresponds tothe light flux, and further, when the first ordered diffracted ray isused, the loss of the light amount is smaller than the case where thehigher ordered diffracted ray corresponds to the light flux.Accordingly, the objective lens 1 of the present embodiment is effectivein the optical pickup apparatus to record the information onto theoptical disk such as the DVD-RAM, into which the high densityinformation is recorded. Further, the diffracted surface is desirable inthat, for the light with 3 different wavelengths, the diffractionefficiency is maximum at the middle wavelength thereof, however, it mayhave the maximum diffraction efficiency at the wavelengths on the bothends thereof.

Further, when the phase difference function of the aspherical surfacerefraction surface and the ring zonal diffraction surface isappropriately designed, the spherical aberration generated by thedifference of the thickness of the transparent substrate 21 of theoptical disk 20 is corrected for each light flux emitted from the firstsemiconductor laser 11, blue laser 12 and second semiconductor laser 13.Further, in the phase difference function to show the position of theannular band formed on the objective lens 1, when the coefficient of thefourth power term and subsequent terms in the power series is used, thechromatic aberration of the spherical aberration can be corrected.Incidentally, as for the third optical disk (CD), the aperture in thepractical use is NA 0.45, and the spherical aberration is correctedwithin NA 0.45, and the spherical aberration in the outside range of NA0.45 is made the flare. The light flux passing through an area within NA0.45 forms the light spot on the information recording surface, and theflare light passing the outside of NA 0.45 passes through a distant areafrom the light spot on the information recording surface so that it doesnot affect badly. According to these corrections, for each optical disk20, the aberration of the light converging spot on the informationrecording surface becomes almost the same degree as the diffractionlimit (0.07 λrms) or lower than that.

In the present embodiment, the diaphragm 3 provided in the optical pathis a diaphragm having the fixed numeral aperture (NA 0.65), andsuperfluous mechanism is not needed, therefore, cost reduction can berealized. Incidentally, when the third disk is recorded and/or playedback, the numeral aperture of the diaphragm 3 may be changeable so thatthe unnecessary light (more than NA 0.45) can be removed. Further, thebeam splitter 67 is used for adjusting the optical axis of each laserlight. The light detector (not shown) may be, as well known,respectively provided for each of light sources, or one light detectormay receive the reflected light corresponding to 3 light sources 11, 12and 13.

Next, the objective lens of the fifth embodiment of the presentinvention will be described.

In the present embodiment, on the ring zonal diffraction surface, only apoint that the phase difference function to express the position of theannular band uses the coefficient of second power term in the powerseries, is different from the objective lens in the above describedfourth embodiment, and thereby, the axial chromatic aberration can alsobe corrected. Further, according to the objective lens of the presentembodiment, in the same manner as the fourth embodiment, for eachoptical disk 20, the aberration of the light converging spot on theinformation recording surface 22 becomes almost the same degree as thediffraction limit (0.07 λ rms) or smaller than that.

Next, the optical pickup apparatus of the sixth embodiment of thepresent invention will be described.

In the optical pickup apparatus of the present embodiment, for the firstoptical disk (for example, DVD) and the second optical disk (forexample, blue laser use next-generation high density optical disk), thelight flux emitted from the light source is made into the parallel lightby the coupling lens, and for the third optical disk (for example, CD),the light flux emitted from the light source is made into the divergentlight by the coupling lens, and these are respectively converged by theobjective lens. The thickness of the transparent substrates 21 of thefirst and the second optical disks is 0.6 mm, and the thickness of thetransparent substrate 21 of the third optical disk is 1.2 mm.

In the present embodiment, both of the spherical aberration of the firstoptical disk and the second optical disk are corrected within thediffraction limit by the effect of the diffraction surface, and for thethird optical disk, the spherical aberration generated by the thicknessof the disk larger than that of the first and second optical disks ismainly cancelled by the spherical aberration generated by entrance ofthe divergent light flux into the objective lens, and the sphericalaberration at the numerical aperture lower than a predeterminednumerical aperture NA necessary for recording/reproducing of the thirdoptical disk, for example, NA 0.5, or NA 0.45, is made to be correctedwithin the diffraction limit.

Accordingly, when, for the optical information recording mediacorresponding to each wavelength of λ₁, λ₂, λ₃ (λ₁<λ₂<λ₃), predeterminednumerical apertures necessary for recording/reproducing them are NA1,NA2 and NA3, for respective wavelengths, RMS of the wave frontaberration can be corrected to a lower value than 0.07 λ₁ within therange of NA1, to a lower value than 0.07 λ₂ within the range of NA2, andto a lower value than 0.07 λ₃ within the range of NA3.

Further, for the third optical disk, it is not preferable that the beamspot diameter becomes too small by the light flux of the numericalaperture NA larger than a predetermined numerical aperture NA.Accordingly, it is preferable that, in the same manner as the fourthembodiment, in the numerical aperture larger than a necessary numericalaperture, the spherical aberration is made the flare.

The above-described optical pickup apparatus having 3 light sources withdifferent wavelength light in the fourth–the sixth embodiments, can bemounted in a recording apparatus for the audio and/or image, or areproducing apparatus for the audio and/or image of a compatible playeror drive, or an AV device in which these are assembled, personalcomputer, and other information terminals, for arbitrary different 2 ormore of, that is, for a plurality of optical information recordingmedia, such as, for example, a CD, CD-R, CD-RW, CD-Video, CD-ROM, DVD,DVD-ROM, DVD-RAM, DVD-R, DVD-RW, MD, etc.

EXAMPLE

Examples of the objective lens of the present invention will bedescribed below.

Examples 1–8

The objective lens in Examples 1–8 is concrete examples of the objectivelens according to the first embodiment, and has the aspherical shapeexpressed by the following [Equation 3] on the refraction surface.

$\begin{matrix}{Z = {\frac{h_{2}/R_{0}}{1 + \sqrt{1 - {\left( {1 + \kappa} \right)\left( {h/R_{0}} \right)^{2}}}} + {\sum\limits_{i = 2}^{\infty}\;{A_{2\; i}h_{2i}}}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$Where, Z is an axis in the optical axis direction, h is an axis in theperpendicular direction to the optical axis (height from the opticalaxis: an advance direction of the light is positive), RO is the paraxialradius of curvature, κ is a conical coefficient, A is an asphericalcoefficient, and 2i is an exponent of the aspherical surface. Further,in Examples 1–3, 6–8, the diffraction surface is expressed by [Equation1] as the phase difference function ΦB in a unit of radian, and in thesame manner, in Examples 4 and 5, the diffraction surface is expressedby [Equation 2] as the optical path difference function Φb in a unit ofmm.

$\begin{matrix}{\Phi_{B} = {\sum\limits_{i - 1}^{\infty}\;{B_{2\; i}h_{21}}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack \\{\Phi_{b} = {\sum\limits_{i = 1}^{\infty}\;{b_{2\; i}h_{2i}}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

Example 1

A view of the optical path of the diffraction optical lens (theobjective lens having the diffraction surface) which is the objectivelens in Example 1, is shown in FIG. 1. A view of the sphericalaberration up to the numerical aperture 0.60 to λ=635 nm for thediffraction optical lens in Example 1, is shown in FIG. 2. Further,views of the spherical aberration up to the numerical apertures 0.45 and0.60 to the wavelength λ=780 nm for the diffraction optical lens inExample 1, are shown in FIG. 3 and FIG. 4. Incidentally, although thediffractive lens shown in FIG. 1 is provided blazed type coaxial annularbands on its entire lens surface, a relief shape of the diffractivesection is omitted in this figure. Also, in the following figures, therelief shape of the diffractive section is omitted.

According to the diffraction optical lens in Example 1, as shown in FIG.2, at all apertures up to NA 0.60 to the wavelength λ=635 nm, there isalmost no aberration. Further, as shown in FIG. 3, to the wavelengthλ=780 nm, up to NA 0.45 which is a range of practical use, there isalmost no aberration. In the portion of NA 0.45–0.60 of the outside ofit, as shown in FIG. 4, the spherical aberration is largely under, andis made the flare. According to this, an appropriate spot diameter canbe obtained.

Views of the wave front aberration to the wavelengths λ=635 nm and λ=780nm of the diffraction lens in Example 1 are respectively shown in FIG. 5and FIG. 6. As can be seen from these views, according to thediffraction optical lens in Example 1, to any wavelength, there is noaberration on the optical axis, and even in the case of the image height0.03, the aberration is on the level of almost no aberration in thepractical use.

Lens data of Example 1 will be shown as follows. In [Table 1], R is theradius of curvature, d is the space between surfaces, n is therefractive index at the main wavelength, and ν is Abbe's number.

Example 1

When the wavelength of the light source λ1=635 nm, the focal distancef1=3.34, the numerical aperture NA1=0.60, infinity specification.

When the wavelength of the light source λ2=780 nm, the focal distancef2=3.36, the numerical aperture NA2=0.45, infinity specification.

In this embodiment, in the light flux of λ1, an amount of +first ordereddiffracted ray is generated to be greater than that of any other ordereddiffracted ray. Also, in the light flux of λ2, an amount of +firstordered diffracted ray is generated to be greater than that of any otherordered diffracted ray. Assuming that the diffracting efficiency of+first ordered diffracted ray for the light flux of λ1 is 100%, thediffracting efficiency for the light flux of λ2 is 84%. Further,assuming that the diffracting efficiency of +first ordered diffractedray for the light flux of λ2 is 100%, the diffracting efficiency for thelight flux of λ1 is 89%.

TABLE 1 Surface No. R d₁ d₂ n₁ n₂ νd nd 1 (Aspherical   2.126 2.2 2.21.53829 1.53388 56 1.5404   surface 1 ·   diffraction   surface) 2(Aspherical −7.370 1.0 1.0   surface 2) 3 Cover glass ∞ 0.6 1.2 1.581391.57346 30 1.585 4 ∞ (Subscript 1 is at λ₁ = 635 nm, subscript 2 is atλ₂ = 780 nm, νd and nd respectively show values to d-line.) Asphericalcoefficient Aspherical surface 1 Aspherical surface 2 κ = −0.10721 κ =−11.653 A4 = −0.0032315 A4 = 0.0038456 A6 = −0.00058160 A6 = −0.020800A8 = −4.6316 × 10⁻⁵ A8 = 0.0078684 A10 = −3.79858 × 10⁻⁵ A10 =−0.0019431 A12 = −6.0308 × 10⁻⁶ A12 = 0.00024343 Diffraction surfacecoefficient B2 = −96.766 B4 = −2.9950 B6 = 2.1306 B8 = −0.12614 B10 =−0.095285

Example 2, Example 3

Next, Example 2 and Example 3 will be described. Views of the opticalpaths of the diffraction optical lens, which is the objective lens inExample 2, to λ=405 nm and 635 nm will be respectively shown in FIG. 7and FIG. 8. Further, in FIG. 9 and FIG. 10, views of the sphericalaberration up to the numerical aperture 0.60 to λ=405 nm and 635 nm forthe diffraction optical lens in Example 2 will be respectively shown.Further, in FIG. 11 and FIG. 12, views of the wave front aberration tothe wavelengths λ=405 nm and 635 nm for the diffraction optical lens inExample 2 will be respectively shown.

Further, in FIG. 13 and FIG. 14, views of the optical paths of thediffraction optical lens, which is the objective lens in Example 3, toλ=405 nm and 635 nm will be respectively shown. Further, in FIG. 15 andFIG. 16, views of the spherical aberration up to the numerical aperture0.60 to λ=405 nm and 635 nm for the diffraction optical lens in Example3 will be respectively shown. Further, in FIG. 17 and FIG. 18, views ofthe wave front aberration to the wavelengths λ=405 nm and 635 nm for thediffraction optical lens in Example 3 will be respectively shown.

In Examples 2 and 3, the thickness of the substrates are both 0.6 mm tothe wavelength λ=405 nm and the wavelength λ=635 nm, and NA is 0.6, andthe wave front aberration is almost no aberration on the optical axis,and even at the image height 0.03 mm, it is on the level of practicallyalmost no-aberration.

Lens data of Examples 2 and 3 will be shown below.

Example 2

When the wavelength of the light source λ1=405 nm, the focal distancef1=3.23, the numerical aperture NA1=0.60, infinite specification.

When the wavelength of the light source λ2=635 nm, the focal distancef2=3.34, the numerical aperture NA2=0.60, infinite specification.

In this embodiment, in the light flux of λ1, an amount of +first ordereddiffracted ray is generated to be greater than that of any other ordereddiffracted ray. Also, in the light flux of λ2, an amount of +firstordered diffracted ray is generated to be greater than that of any otherordered diffracted ray.

TABLE 2 Surface No. R d₁ d₂ n₁ n₂ νd nd 1 (Aspherical   2.128 2.2 2.21.55682 1.53829 56 1.5405   surface 1 ·   diffraction   surface) 2(Aspherical −7.359 1.0 1.0   surface 2) 3 Cover glass ∞ 0.6 0.6 1.622301.58139 30 1.585 4 ∞ (Subscript 1 is at λ₁ = 405 nm, subscript 2 is atλ₂ = 635 nm, νd and nd respectively show values to d-line.) Asphericalcoefficient Aspherical surface 1 Aspherical surface 2 κ = −0.15079 κ =−3.8288 A4 = −0.0021230 A4 = 0.0036962 A6 = −0.00076528 A6 = −0.020858A8 = −8.84957 × 10⁻⁵ A8 = 0.0079732 A10 = −3.49803 × 10⁻⁵ A10 =−0.0018713 A12 = −2.38916 × 10⁻⁶ A12 = 0.00022504 Diffraction surfacecoefficient B2 = 0.0 B4 = −6.7169 B6 = 2.0791 B8 = −0.31970 B10 =0.00016708

Example 3

When the wavelength of the light source λ1=405 nm, the focal distancef1=3.31, the numerical aperture NA1=0.60, infinite specification.

When the wavelength of the light source λ2=635 nm, the focal distancef2=3.34, the numerical aperture NA2=0.60, infinite specification.

In this embodiment, in the light flux of λ1, an amount of +first ordereddiffracted ray is generated to be greater than that of any other ordereddiffracted ray. Also, in the light flux of λ2, an amount of +firstordered diffracted ray is generated to be greater than that of any otherordered diffracted ray.

TABLE 3 Surface No. R d₁ d₂ n₁ n₂ νd nd 1 (Aspherical   2.300 2.2 2.21.55682 1.53829 56 1.5404   surface 1 ·   diffraction   surface) 2(Aspherical −7.359 1.0 1.0   surface 2) 3 Cover glass ∞ 0.6 0.6 1.622301.58139 30 1.585 4 ∞ (Subscript 1 is at λ₁ = 405 nm, subscript 2 is atλ₂ = 635 nm, νd and nd respectively show values to d-line.) Asphericalcoefficient Aspherical surface 1 Aspherical surface 2 κ = −0.19029 κ =6.4430 A4 = 0.00030538 A4 = 0.037045 A6 = −0.0010619 A6 = −0.021474 A8 =−7.5747 × 10⁻⁵ A8 = 0.0078175 A10 = −6.7599 × 10⁻⁵ A10 = −0.0016064 A12= −3.3788 × 10⁻⁶ A12 = 0.00014332 Diffraction surface coefficient B2 =−96.766 B4 = −2.9950 B6 = −0.25560 B8 = −0.08789 B10 = 0.014562

Example 4, Example 5

Next, Example 4 and Example 5 on which the chromatic aberrationcorrection is conducted, will be described. Views of the optical pathsof the diffraction optical lens, which is the objective lens in Example4, will be respectively shown in FIG. 19. Further, in FIG. 20, views ofthe spherical aberration up to the numerical aperture 0.50 to λ=635 nm,650 nm and 780 nm for the diffraction optical lens in Example 4 will berespectively shown. Further, in FIG. 21, views of the optical paths ofthe diffraction optical lens, which is the objective lens in Example 5,will be respectively shown. Further, in FIG. 22, views of the sphericalaberration up to the numerical aperture 0.50 to λ=635 nm, 650 nm and 780nm for the diffraction optical lens in Example 5 will be respectivelyshown.

As can be seen from FIG. 20 and FIG. 22, according to the diffractionoptical lens in Examples 4 and 5, to the wavelength λ=635 nm and thewavelength λ=780 nm, slippage due to color is almost perfectlycorrected, and to the wavelength λ=650 nm, it is also corrected to thedegree of practically no-problem.

Lens data of Examples 4 and 5 will be shown below.

Example 4

When the wavelength of the light source λ1=635 nm, the focal distancef1=3.40, the numerical aperture NA1=0.50, infinite specification.

When the wavelength of the light source λ2=780 nm, the focal distancef2=3.41, the numerical aperture NA2=0.50, infinite specification.

In this embodiment, in the light flux of λ1, an amount of +first ordereddiffracted ray is generated to be greater than that of any other ordereddiffracted ray. Also, in the light flux of λ2, an amount of +firstordered diffracted ray is generated to be greater than that of any otherordered diffracted ray.

TABLE 4 Surface No. R d₁ d₂ n₁ n₂ νd nd 1 (Aspherical   2.442 1.90 1.901.5417 1.5373 56 1.5438   surface 1 ·   diffraction   surface) 2(Aspherical −5.990 1.68 1.68   surface 2) 3 Cover glass ∞ 1.20 1.201.5790 1.5708 30 1.5830 4 ∞ (Subscript 1 is at λ₁ = 635 nm, subscript 2is at λ₂ = 780 nm, νd and nd respectively show values to d-line.)Aspherical coefficient Aspherical surface 1 Aspherical surface 2 κ =−0.53245 κ = 7.3988 A4 = 0.24033 × 10⁻² A4 = 0.90408 × 10⁻² A6 =−0.91472 × 10⁻³ A6 = −0.18704 × 10⁻² A8 = 0.15590 × 10⁻⁴ A8 = −0.47368 ×10⁻³ A10 = −0.11131 × 10⁻³ A10 = 0.16891 × 10⁻³ Diffraction surfacecoefficient b2 = −0.36764 × 10⁻² b4 = −0.91727 × 10⁻⁴ b6 = −0.34903 ×10⁻⁴ b8 = 0.77485 × 10⁻⁵ b10 = −0.15750 × 10⁻⁵

Example 5

When the wavelength of the light source λ1=635 nm, the focal distancef1=3.40, the numerical aperture NA1=0.50, infinite specification.

When the wavelength of the light source λ2=780 nm, the focal distancef2=3.40, the numerical aperture NA2=0.50, infinite specification.

In this embodiment, in the light flux of λ1, an amount of +first ordereddiffracted ray is generated to be greater than that of any other ordereddiffracted ray. Also, in the light flux of λ2, an amount of +firstordered diffracted ray is generated to be greater than that of any otherordered diffracted ray.

TABLE 5 Surface No. R d₁ d₂ n₁ n₂ νd nd 1 (Aspherical   2.160 1.80 1.801.5417 1.5373 56 1.5438   surface 1 ·   diffraction   surface) 2(Aspherical −11.681 1.64 1.64   surface 2) 3 Cover glass ∞ 1.20 1.201.5790 1.5708 30 1.5830 4 ∞ (Subscript 1 is at λ₁ = 635 nm, subscript 2is at λ₂ = 780 nm, νd and nd respectively show values to d-line.)Aspherical coefficient Aspherical surface 1 Aspherical surface 2 κ =−0.17006 κ = −40.782 A4 = −0.30563 × 10⁻² A4 = 0.73447 × 10⁻² A6 =−0.45119 × 10⁻³ A6 = 0.85177 × 10⁻³ A8 = 0.58811 × 10⁻⁵ A8 = −0.82795 ×10⁻³ A10 = −0.13002 × 10⁻⁴ A10 = 0.23029 × 10⁻³ Diffraction surfacecoefficient b2 = −0.74461 × 10⁻² b4 = 0.11193 × 10⁻² b6 = −0.85257 ×10⁻³ b8 = 0.50517 × 10⁻³ b10 = −0.11242 × 10⁻³

Examples 6–8

Next, Examples 6–8 will be described. Views of the optical paths of thediffraction optical lenses, which are the objective lenses in Examples6–8, to λ=650 nm will be respectively shown in FIG. 23, FIG. 30 and FIG.37. Further, in FIG. 24, FIG. 31 and FIG. 38, views of the optical pathsof the diffraction optical lenses in Example 6–8, to λ=780 nm (NA=0.5)will be respectively shown. Further, in FIG. 25, FIG. 32 and FIG. 39,views of the spherical aberration up to the numerical aperture 0.60 toλ=650±10 nm for the diffraction optical lenses in Examples 6–8 will berespectively shown. Further, in FIG. 26, FIG. 33 and FIG. 40, views ofthe spherical aberration up to the numerical aperture 0.50 to λ=780±10nm for the diffraction optical lenses in Examples 6–8 will berespectively shown. Further, in FIG. 27, FIG. 34 and FIG. 41, views ofthe spherical aberration up to the numerical aperture 0.60 to λ=780 nmfor the diffraction optical lenses in Examples 6–8 will be respectivelyshown.

Further, in FIG. 28, FIG. 35 and FIG. 42, views of the wave frontaberration rms to λ=650 nm for the diffraction optical lenses inExamples 6–8 will be respectively shown. Further, in FIG. 29, FIG. 36and FIG. 43, views of the wave front aberration rms to λ=780 nm for thediffraction optical lenses in Examples 6–8 will be respectively shown.Further, in FIG. 44, FIG. 45 and FIG. 46, graphs showing therelationship between the number of diffraction annular bands and theheight from the optical axis, for the diffraction optical lenses inExamples 6–8 will be respectively shown. Herein, the number ofdiffraction annular bands is defined as a value in which the phasedifference function is divided by 2π.

In Examples 6–8, as shown in the view of spherical aberration, at allapertures up to NA 0.60 to the wavelength λ=650 nm, there is almost noaberration. Further, to the wavelength λ=780 nm, up to NA 0.50 which isa range of practical use, there is almost no aberration, however, in theportion of NA 0.50–0.60 of the outside of it, the spherical aberrationis large, and it becomes the flare. According to this, to the wavelengthλ=780 nm, an appropriate spot diameter can be obtained.

Next, lens data in Examples 6=8 will be shown. In [Table 6]–[Table 8],STO expresses the diaphragm, and IMA expresses the image surface and isexpressed in the form including the diaphragm.

Example 6

When the wavelength of the light source λ=650 nm, the focal distancef=3.33, the image side numerical aperture NA=0.60, infinitespecification.

When the wavelength of the light source λ=780 nm, the focal distancef=3.37, the image side numerical aperture NA=0.50 (NA=0.60), infinitespecification. When a diameter of 13.5%-strength beam of 780 nm lightflux on the image forming surface is w, w=1.20 μm.

In this embodiment, as shown in FIG. 44, in the central section where aheight from the optical axis is almost smaller than half of theeffective radius in the light flux of λ1 and the light flux of λ2, anamount of −first ordered diffracted ray is generated so as to be greaterthan that of any other ordered diffracted ray, and in the peripheralsection where a height from the optical axis is almost larger than halfof the effective radius, an amount of +first ordered diffracted ray isgenerated so as to be greater than that of any other ordered diffractedray. However, in the present embodiment, it may be possible that thesame ordered diffractive ray of the high order may be generated bymultiplying the pitch of annular bands with an integer instead of − or +first ordered diffracted ray.

Further, in the present embodiment, as shown in FIG. 27, in the secondoptical information recording medium, the spherical aberration atNA1=0.6 is +29 μm, and the spherical aberration at NA2=0.5 is +1 μm.

Further, in the present invention, the pitch of the diffractive portionat NA=0.4 is 14 μm.

TABLE 6 Surface No. R d n(λ = 650 nm) n(λ = 780 nm) OBJ InfinityInfinity STO Infinity 0.0 2 (Aspheric 2.057515 2.2 1.54113 1.53728surface 1 Diffraction surface) 3 (Aspheric −7.8997731 1.0287 surface 2)4 Infinity d4 1.57789 1.57079 5 Infinity d5 IMA Infinity d4 d5 For λ =650 nm 0.6 0.7500 For λ = 780 nm 1.2 0.35 Aspherical coefficientAspherical surface 1 Aspherical surface 2 κ = −1.7952 κ = −3.452929 A4 =0.51919725 × 10⁻² A4 = 0.15591292 × 10⁻¹ A6 = 0.10988861 × 10⁻² A6 =−0.44528738 × 10⁻² A8 = −0.44386519 × 10⁻³ A8 = 0.65423404 × 10⁻³ A10 =5.4053137 × 10⁻⁵ A10 = −4.7679992 × 10⁻⁵ Diffraction surface coefficientB2 = 29.443104 B4 = −14.403683 B6 = 3.9425951 B8 = −2.1471955 B10 =0.31859248

Example 7

When the wavelength of the light source λ=650 nm, the focal distancef=3.33, the image side numerical aperture NA=0.60, infinitespecification.

When the wavelength of the light source λ=780 nm, the focal distancef=3.37, the image side numerical aperture NA=0.50 (NA=0.60), infinitespecification.

In this embodiment, as shown in FIG. 45, in the entire section, anamount of +first ordered diffracted ray is generated so as to be greaterthan that of any other ordered diffracted ray in the light flux of λ1and the light flux of λ2. However, in the present embodiment, it may bepossible that the same ordered diffractive ray of the high order may begenerated by multiplying the pitch of annular bands with an integerinstead of +first ordered diffracted ray.

TABLE 7 Surface No. R d n(λ = 650 nm) n(λ = 780 nm) OBJ Infinity d0 STOInfinity 0.0 2 (Aspheric   2.145844 2.2 1.54113 1.53728 surface 1Diffraction surface) 3 (Aspheric −7.706496 1.0326 surface 2) 4 Infinityd4 1.57789 1.57079 5 Infinity d5 IMA Infinity d d4 d5 For λ = 650 nmInfinity 0.60 0.70 For λ = 780 nm 64.5 1.20 0.35 Aspherical coefficientAspherical surface 1 Aspherical surface 2 κ = −1.801329 κ = −8.871647 A4= 0.1615422 × 10⁻¹ A4 = 0.1492511 × 10⁻¹ A6 = −0.4937969 × 10⁻³ A6 =−0.4447445 × 10⁻² A8 = 0.11038322 × 10⁻³ A8 = 0.60067143 × 10⁻³ A10 =−2.1823306 × 10⁻⁵ A10 = −3.4684206 × 10⁻⁵ Diffraction surfacecoefficient B2 = −17.150237 B4 = −4.1227045 B6 = 1.1902249 B8 =−0.26202222 B10 = 0.018845315

Example 8

For light source wavelength λ=650 nm Focal distance f=3.33 Image sidenumerical aperture NA=0.60 Infinity specification

For light source wavelength λ=780 nm Focal distance f=3.35 Image sidenumerical aperture NA=0.50 (NA=0.60) Infinity specification w (Diameterof a beam of 13.5% intensity on an image forming plane of a light fluxhaving a wavelength of 780 nm)=1.27 μm

In this embodiment, as shown in FIG. 46, in the light flux of λ1 and thelight flux of λ2, in only the extremely peripheral section, an amount of−first ordered diffracted ray is generated so as to be greater than thatof any other ordered diffracted ray and in the other section, an amountof +first ordered diffracted ray is generated so as to be greater thanthat of any other ordered diffracted ray. However, in the presentembodiment, it may be possible that the same ordered diffractive ray ofthe high order may be generated by multiplying the pitch of annularbands with an integer instead of − or +first ordered diffracted ray.

Further, in the present embodiment, as shown in FIG. 41, in the secondoptical information recording medium, the spherical aberration atNA1=0.6 is +68 μm, and the spherical aberration at NA2=0.5 is +9 μm.

Further, the pitch at NA=0.4 is 61 μm.

TABLE 8 Surface No. R d n(λ = 650 nm) n(λ = 780 nm) OBJ Infinity d0 STOInfinity 0.0 2 (Aspheric 2.10598 2.2 1.54113 1.53728 surface 1Diffraction surface) 3 (Aspheric −7.90392 1.0281 surface 2) 4 Infinityd4 1.57789 1.57079 5 Infinity d5 IMA Infinity d4 d5 For λ = 650 nm 0.60.70 For λ = 780 nm 1.2 0.34 Aspheric surface coefficient Asphericsurface 1 κ = −1.2532 A4 = 0.1007 × 10⁻¹ A6 = −0.85849 × 10⁻³ A8 =−0.1.5773 × 10⁻⁵ A10 = 3.2855 × 10⁻⁵ Aspheric surface 2 K = −9.151362 A4= 0.133327 × 10⁻¹ A6 = −0.378682 × 10⁻² A8 = 0.3001 × 10⁻³ A10 = 4.02221× 10⁶ Diffraction surface coefficient B2 = 3.4251 × 10⁻²¹ B4 = 0.0763977B6 = −5.5386 B8 = 0.05938 B10 = 0.2224

Now, causes for fluctuation of a wavelength of a semiconductor laserbeam which enters a lens will be considered based on Examples 6–8. It isconsidered that individual dispersion of a wavelength of a semiconductorlaser is ±2−±3 nm, a width of multi-mode oscillation is about ±2 nm, anda mode hop for writing is about 2 nm. There will be explained anoccasion wherein fluctuation of spherical aberration of a lens caused bywavelength fluctuation of a semiconductor laser which is also caused bythe causes stated above.

When a thickness of a transparent substrate of an optical disk isdifferent respectively for two light sources each having a differentwavelength, a lens corrected to be no-aberration for infinite light(parallel light flux) emitted from each of two light sources each havinga different wavelength has relatively large fluctuation of sphericalaberration, compared with wavelength fluctuation of about 10 nm for onelight source, as understood from data concerning Example 6. In Example6, though the wave-front aberration is 0.001 λrms in the wavelength of650 nm, it is deteriorated to about 0.035 λrms in the wavelength of 640nm and 660 nm. For an optical system with well-controlled laserwavelength, Example 6 can naturally be put to practical usesufficiently. On the contrary, in the case of a lens which is almostno-aberration for infinite light from either one light source and iscorrected to be almost no-aberration for finite light (non-parallellight flux) from the other wavelength light source, like the lens inExample 7, it is possible to control the spherical aberrationfluctuation to be extremely small, for wavelength fluctuation of about10 nm for one light source.

Next, temperature-caused capacity fluctuation of a diffraction opticalsystem (optical system having a diffraction optical lens) of the presentembodiment will be explained. First, a wavelength of a semiconductorlaser has a tendency to extend by 6 nm when temperature rises by 30° C.On the contrary, when a diffraction optical system is composed of aplastic lens, the index of refraction has a tendency to be reduced byabout 0.003–0.004 when temperature rises by 30° C. In the case of a lenscorrected to be no-aberration for infinite light for any of twowavelengths like that in Example 6, a factor of a wavelength of asemiconductor laser caused by temperature change and a factor of theindex of refraction of a plastic lens caused by temperature changedisplay effect of mutual compensation, and make it possible to create anoptical system which is extremely resistant to temperature change.Further, in Example 6, even when raw material is glass, it is possibleto create an optical system having an allowable range for temperaturechange. Further, even in the case of Example 7, deterioration ofwave-front aberration is about 0.035 λrms for the temperature change of30° C. to be sufficient temperature compensation for practical use,which, however, is behind Example 6.

The compensation effect of temperature change stated above will furtherbe explained. When recording and/or reproduction is conducted on twotypes of optical information recording media each having a transparentsubstrate with a different thickness by two light sources each having adifferent wavelength, it is possible to obtain image formingcharacteristic which is the same as an exclusive objective lens, becauseit is possible to make the rms value of wave-front aberration to be 0.07of each wavelength or less even in the case of a numerical aperturerequired for information recording surface on each optical disk or inthe case of a numerical aperture equal to or greater than the aforesaidaperture, by using an objective lens having a diffraction pattern. Inordered to make an optical pickup apparatus which is inexpensive andcompact, a semiconductor laser is commonly used as a light source, and aplastic lens is commonly used as an objective lens.

There are various types of plastic materials which are used as a lens,but their refractive index changes caused by temperature change andtheir coefficient of linear expansion are greater than those of glass.In particular, the refractive index changes caused by temperature changehave an influence on various characteristics of a lens. In the case of aplastic material used as an optical element of an optical pickup, therefractive index change caused by temperature change in the vicinity of25° C. is −0.0002/° C.–−0.00005/° C. Further, −0.0001/° C. is for themost of materials having low double refraction. Refractive index changesof thermosetting plastics used as a lens which are caused by temperaturechange are further greater, and some of them exceed the aforesaid range.

Even in the case of a semiconductor laser, an oscillation wavelength isdependent on temperature, as far as those manufactured by the presenttechnology are concerned, the oscillation wavelength change caused bytemperature change in the vicinity of 25° C. is 0.05 nm/° C.–0.5 nm/° C.

When a wave-front aberration of a light flux for reproducing informationon an optical information recording medium or for recording informationon an optical information recording medium is changed by temperature tocause an rms value to be 0.07 or more, it is difficult to maintain thecharacteristics as an optical pickup apparatus. In the case of theoptical information medium of high density, in particular, it isnecessary to pay attention to the change of wave-front aberration causedby temperature. In the case of a wave-front aberration change of aplastic lens caused by temperature change, both of a shift of focus anda change of spherical aberration are caused by this wave-frontaberration change, but the latter is important because the focus controlis conducted in an optical pickup apparatus for the former. In thiscase, when the plastic material satisfies the relationship of−0.0002/° C.<Δn/ΔT<−0.00005/° C.when ΔT represents an amount of a change of a refractive index for thetemperature change ΔT (° C.), and when a semiconductor laser satisfiesthe relationship of0.05 nm/° C.<Δλ1/ΔT<0.5 nm/° C.when Δλ1 represents an amount of a change of oscillation wavelength forthe temperature change ΔT, fluctuations of wave-front aberration causedby refractive index change of a plastic lens caused by temperaturechange and fluctuations of wave-front aberration caused by a wavelengthchange of the semiconductor laser caused by temperature change act tocontradict mutually, thereby, an effect of compensation can be obtained.

When an amount of change of a component of cubic spherical aberration ofwave-front aberration for ambient temperature change of ΔT (° C.) isrepresented by ΔWSA3 (λrms), this is proportional to the fourth power ofa numerical aperture (NA) of an objective lens on the opticalinformation medium side for a light flux passing through the objectivelens as well as to focal distance f (mm) of the plastic lens, and isinversely proportional to wavelength λ (mm) of the light source becausethe wave-front aberration is evaluated in a unit of wavelength.Therefore, the following expression holds,ΔWSA3=k·(NA)⁴ ·f·ΔT/λ  (a1)wherein, k represents an amount which is dependent on a type of anobjective lens. Incidentally, a plastic double aspherical objective lensoptimized under the conditions that a focal distance is 3.36 mm, anumerical aperture on the optical information medium side is 0.6, and anincident light flux is a collimated light is described in MOC/GRIN'97Technical Digest C5 p40–p43, “The Temperature characteristics of a newoptical system with quasi-finite conjugate plastic objective for highdensity optical disk use” It is estimated that the wavelength λ is 650nm, because the graph in this document shows that WSA3 varies by 0.045λrms for the temperature change of 30° C., and thereby, the objectivelens is considered to be used for DVD. When the data stated above aresubstituted in expression (a1), k=2.2×10⁻⁶ is obtained. Though there isno description about an influence of wavelength change caused bytemperature change, when a change of oscillation wavelength is small, aninfluence of refractive index caused by temperature change is greater asfar as the objective lens using no diffraction is concerned.

With regard to the optical pickup apparatus for recording and/orreproducing concerning DVD, it is necessary that k is not more than theabove-mentioned value. When recording and/or reproducing for two typesof optical information recording media each having a transparentsubstrate with a different thickness, one can not ignore an influence ofwavelength change caused by temperature change, in an objective lenshaving a diffraction pattern. With regard to k, in particular, the valueof k varies depending on a focal distance, a refractive index change ofa plastic material caused by temperature change, a thickness differencebetween transparent substrates and a difference of oscillationwavelength between two light sources, and in Example 6, both a maincause of wavelength change of a semiconductor laser caused bytemperature change and a main cause of a refractive index change of aplastic lens caused by temperature change act to be effective forcompensation, and even when the objective lens is a plastic lens, achange of wave-front aberration caused by temperature change is small,resulting in k=2.2×10⁻⁶/° C. and k=0.4×10⁻⁶/° C. in simulation.

It is possible for k to take a range of 0.3<k<2.2. Therefore, fromexpression (a1), the following holds.k=ΔWSA3·λ/{f·(NA1)⁴ ·ΔT(NA)}  (a2)

Therefore, the following holds.0.3×10⁻⁶/° C.<ΔWSA3·λ/{f·(NA1)⁴ ·ΔT}<2.2×10⁻⁶/° C.  (a3)In expression (a3), when the value of k exceeds the upper limit, it isdifficult to maintain characteristics of an optical pickup apparatus dueto temperature change, while when the lower limit is exceeded, it tendsto be difficult to maintain characteristics of an optical pickupapparatus in the case where a wavelength only is changed, thoughvariation for temperature change is small.

In Example 8, by worsening efficiency of wavelength on one side, namely,of wavelength of 780 nm, slightly within an allowable range, comparedwith Example 6, it is possible to make the spherical aberrationvariation at ±10 nm in the vicinity of the wavelength on the other side,namely, of the wavelength of 650 nm to be small. Though wave-frontaberration at wavelength of 640 nm or 660 nm is about 0.035 λrms inExample 6, wave-front aberration at wavelength of 640 nm or 660 nm canbe improved to about 0.020 λrms in Example 8. These two factors are inthe relationship of trade-off, and it is important to have a balance,and when 0.07 λrms is exceeded, lens performance is deteriorated and itis difficult to use as an optical system for an optical disk.

Now, the relationship between diffraction power and a lens shape will beexplained. In FIG. 47, the relationship between diffraction power and alens shape is shown illustratively. FIG. 47( a) is a diagram showingthat diffraction power is a positive lens shape at all portions, while,FIG. 47( b) is a diagram showing that diffraction power is a negativelens shape at all portions. As shown in FIG. 47( c), a lens in FIG. 6 isdesigned so that diffraction power is negative in the vicinity of anoptical axis and is changed to be positive on the half way. Due to this,it is possible to prevent diffracting annular band whose pitch is toofine. Further, by designing a lens so that diffraction power is changedfrom the positive power to the negative one in the vicinity of aperipheral portion of the lens as shown in FIG. 8, it is also possibleto obtain satisfactory aberration between two wavelengths. It ispossible to arrange so that diffraction power is positive in thevicinity of an optical axis and is changed to the negative power on thehalf way, for example, as shown in FIG. 47( d).

In FIG. 47( c), a diffraction surface has plural diffracting annularbands which are blazed, and a step portion of the diffracting annularband which is closer to an optical axis is located to be away from theoptical axis, and a step portion of the diffracting annular band whichis away from an optical axis is located to be closer to the opticalaxis. In FIG. 47( d), a diffraction surface has plural diffractingannular bands which are blazed, and a step portion of the diffractingannular band which is closer to an optical axis is located to be closerto the optical axis, and a step portion of the diffracting annular bandwhich is away from an optical axis is located to be away from theoptical axis.

Examples 9 and 10

An objective lens in Examples 9 and 10 has on its refraction surface anaspherical shape shown by expression (a3), and Example 9 is a finiteconjugate type complying with two light sources, and Example 10 is aconcrete example of an objective lens related to the second embodimentand is a finite conjugate type complying with three light sources. InExamples 9 and 10, the diffraction surface is expressed by expression(a1) as phase difference function ΦB wherein a unit is radian.

FIGS. 50 and 51 show optical paths of the objective lens in Example 9for λ=650 nm and λ=780 nm. FIG. 52 shows a diagram of sphericalaberration covering up to numerical aperture 0.60 of the objective lensin Example 9 for λ=650 nm. FIGS. 53 and 54 show diagrams of sphericalaberration covering up to numerical apertures 0.45 and 0.60 of theobjective lens in Example 9 for λ=780 nm. FIGS. 55 and 56 show diagramsof wave-front aberration of the objective lens in Example 9 forwavelength λ=650 nm and λ=780 nm.

FIGS. 57–59 show optical paths of the objective lens in Example 10 forλ=650 nm, λ=400 nm and λ=780 nm. FIGS. 61 and 61 show diagrams ofspherical aberration covering up to numerical apertures 0.65 of theobjective lens in Example 10 for λ=650 nm and λ=400 nm. FIGS. 62 and 63show diagrams of spherical aberration covering up to numerical apertures0.45 and 0.65 of the objective lens in Example 10 for λ=780 nm. FIGS.64–66 show wave-front aberration diagrams of the objective lens inExample 10 for λ=650 nm, =400 nm and λ=780 nm.

According to an objective lens in each of Examples 9 and 10, in any ofthe examples, a light flux exceeding NA 0.45 in practical use causeslarge spherical aberration for light with wavelength of 780 nm, and itdoes not contribute to recording and/or reproduction of information, asa flare.

Lens data of Examples 9 and 10 will be shown as follows. In Table 9 andTable 10, r represents a radius of curvature of the lens, d represents adistance between surfaces, n represents a refractive index at eachwavelength, and ν represents Abbe's number. As a reference, there willbe described the refractive index for d line (λ=587.6 nm) and νd (Abbe'snumber). The figure for the surface number is shown including anaperture, and in the present example, an air space is divided, forconvenience' sake, into two locations before and after the portioncorresponding to the transparent substrate of an optical disk.

Example 9

-   f=3.33 Image side NA 0.60 Magnification −0.194 (for wavelength λ=650    nm)-   f=3.35 Image side NA 0.45 (NA 0.60) Magnification −0.195 (for    wavelength λ=780 nm)

TABLE 9 nd νd Surface No. r d n n (Reference) Light source • 20.0Aperture • 0.0 2 (Aspheric 2.2 1.53771 1.5388 1.5404 56.0   surface 1 ·  Diffraction   surface) 2 (Aspheric 1.7467 1.58030 1.57346 1.585 29.9  surface 2) 4 • d4 5 • d5 Image point • d4 d5 for λ = 650 nm 0.6 0.7500for λ = 780 nm 1.2 0.3964 Aspheric surface 1 κ = −0.1295292 A4 =−0.045445253 A8 = −0.00011777995 A10 = −5.3843777 × 10⁻⁵ A12 =−9.0807729 ×10⁻⁶ Diffraction surface 1 B2 = 0 B4 = −7.6489594 B6 =0.9933123 B8 = −0.28305522 B10 = 0.011289605 Aspheric surface 2 A4 =0.019003845 A6 = −0.010002187 A8 = 0.004087239 A10 = −0.00085994626 A12= 7.5491556 × 10⁻⁵

Example 10

$\begin{matrix}{f = {{3.31\mspace{14mu}\begin{matrix}{{Image}\mspace{14mu}{side}} \\{{NA}\mspace{14mu} 0.65}\end{matrix}\mspace{14mu}{Magnification}}\mspace{14mu} - {0.203\mspace{14mu}\begin{matrix}\begin{matrix}\left( {for} \right. \\{wavelength}\end{matrix} \\\left. {\lambda = {650\mspace{14mu}{nm}}} \right)\end{matrix}}}} \\{f = {{3.14\mspace{14mu}\begin{matrix}{{Image}\mspace{14mu}{side}} \\{{NA}\mspace{14mu} 0.65}\end{matrix}\mspace{14mu}{Magnification}}\mspace{14mu} - {0.190\mspace{14mu}\begin{matrix}\begin{matrix}\left( {for} \right. \\{wavelength}\end{matrix} \\\left. {\lambda = {400\mspace{14mu}{nm}}} \right)\end{matrix}}}} \\{f = {{3.34\begin{matrix}{{Image}\mspace{14mu}{side}} \\{{NA}\mspace{14mu} 0.65}\end{matrix}\mspace{14mu}{Magnification}}\mspace{14mu} - {0.205\mspace{14mu}\begin{matrix}\begin{matrix}\left( {for} \right. \\{wavelength}\end{matrix} \\\left. {\lambda = {780\mspace{14mu}{nm}}} \right)\end{matrix}}}}\end{matrix}$

TABLE 10 n n n (λ = (λ = (λ = Surface No. r d 650 nm) 400 nm) 780 nm)Light ∞ 20.0 source Aperture ∞ 0.0 2 (Aspheric 2.450359 2.2 1.877071.92261 1.86890   surface 1   Diffraction   surface 1) 3 (Aspheric9.108348 1.4503   surface 2   Diffraction   surface 2) 4 ∞ d4 1.580301.62441 1.57346 5 ∞ d5 Image point ∞ for λ = 650 nm for λ = 400 nm for λ= 780 nm d4 0.6 0.6 1.2 d4 0.7500 0.5540 0.4097 Aspheric surface 1 κ =−0.08796008 A4 = −0.010351744 A6 = 0.0015514472 A8 = −0.00043894535 A10= 5.481801 × 10⁻⁵ A12 = −4.2588508 × 10⁻⁶ Diffraction surface 1 B2 = 0B4 = −61.351934 B6 = 5.9668445 B8 = −1.2923244 B10 = 0.041773541Aspheric surface 2 κ = −302.6352 A4 = 0.002 A6 = −0.0014 A8 = 0.0042 A10= −0.0022 A12 = 0.0004 Diffraction surface 2 B2 = 0 B4 = 341.19136 B6 =−124.16233 B8 = 49.877242 B10 = −5.9599182

Incidentally, the concrete example of the objective lens in the Example10 can also be applied equally to the third embodiment.

Examples 11–14

An objective lens in each of Examples 11–14 has on its refractionsurface an aspherical shape shown by expression (a3). In Examples 11–13,the diffraction surface is expressed by expression (a1) as phasedifference function ΦB wherein a unit is radian. In Example 14, thediffraction surface is expressed by expression (a2) as optical pathdifference function Φb wherein a unit is mm.

When obtaining characteristics of an objective lens in each of theExamples 11–14, a light source wavelength for the first optical disk(DVD) is made to be 650 nm, a light source wavelength for the secondoptical disk (advanced high density optical disk employing blue laser)is made to be 400 nm, and transparent substrate thickness t1 for both ofthe first optical disk and the second optical disk is 0.6 mm. The lightsource wavelength for the third optical disk (CD) having transparentsubstrate thickness t2 which is different from t1 and is 1.2 mm was madeto be 780 nm. Numerical apertures NA corresponding respectively to lightsource wavelengths 400 nm, 650 nm and 780 nm are assumed to be 0.65,0.65 and 0.5.

Example 11

Example 11 is a concrete example of an objective lens related to thefourth embodiment, and it is structured so that a collimated lightenters the objective lens. In this example, the square terms are notincluded in coefficients of the phase difference function, andcoefficients of terms other than the square terms only are used.

FIGS. 68–70 show diagrams for the optical path of the objective lens inExample 11 respectively for λ=650 nm. λ=400 nm and λ=780 nm. FIG. 71 andFIG. 72 show the diagrams of spherical aberration of the objective lensin Example 11 up to numerical aperture 0.65, respectively for λ=650 nmand λ=400 nm. FIG. 73 and FIG. 74 show the diagrams of sphericalaberration of the objective lens in Example 11 up to numerical aperture0.45 and numerical aperture 0.65, for wavelength λ=780 nm. FIGS. 75–77show diagrams of spherical aberration of the objective lens in Example11 respectively for λ=650 nm, =400 nm and λ=780 nm.

Lens data of Example 11 will be shown as follows. In Table 11, rrepresents a radius of curvature of the lens, d represents a distancebetween surfaces and n represents a refractive index at each wavelength.The figure for the surface number is shown including an aperture.

Example 11

-   f=3.33 Image side NA 0.65 (for wavelength λ=650 nm)-   f=3.15 Image side NA 0.65 (for wavelength λ=400 nm)-   f=3.37 Image side NA 0.45 (for wavelength λ=780 nm) (NA 0.65)

TABLE 11 n n n (λ = (λ = (λ = Surface No. r d 650 nm) 400 nm) 780 nm)Aperture ∞ 0.0 2 (Aspheric 2.177303 2.2 1.80256 1.84480 1.79498  surface 1   Diffraction   surface 1) 3 (Aspheric 6.457315 0.6985  surface 2   Diffraction   surface 2) 4 ∞ d4 1.58030 1.62441 1.57346 5∞ d5 Image point ∞ for λ = 650 nm for λ = 400 nm for λ = 780 nm d4 0.60.6 1.2 d4 0.7500 0.6228 0.3995 Aspheric surface 1 κ = −0.1847301 A4 =−0.0090859227 A6 = 0.0016821871 A8 = −0.0071180761 A10 = 0.00012406905A12 = −1.4004589 × 10⁻⁵ Diffraction surface 1 B2 = 0 B4 = −69.824562 B6= 0.35641549 B8 = 0.6877372 B10 = −0.18333885 Aspheric surface 2 κ =−186.4056 A4 = 0.002 A6 = −0.0014 A8 = 0.0042 A10 = −0.0022 A12 = 0.0004Diffraction surface 2 B2 = 0 B4 = 745.72117 B6 = −334.75078 B8 =81.232224 B10 = −5.3410176

In an optical pickup apparatus having therein an objective lens likethat in Example 11 (and Example 12 which will be described later) andthree light sources, it is possible to correct spherical aberrationcaused by the difference of transparent substrate thickness andchromatic aberration of spherical aberration caused by the difference ofwavelength for each disk, by designing aspherical surface coefficientsand coefficients of a phase difference function. As is clear from FIG.74, an outside of the numerical aperture NA 0.45 in practical use ismade to be flare on the third optical disk.

Example 12

An objective lens of Example 12 is structured so that diverged lightfrom a finite distance may enter the objective lens. In this example,the square terms are not included in coefficients of the phasedifference function, and coefficients of terms other than the squareterms only are used.

FIGS. 78–80 show diagrams for the optical path of the objective lens inExample 12 respectively for λ=650 nm. λ=400 nm and λ=780 nm. FIG. 81 andFIG. 82 show the diagrams of spherical aberration of the objective lensin Example 12 up to numerical aperture 0.65, respectively for λ=650 nmand λ=400 nm. FIG. 83 and FIG. 84 show the diagrams of sphericalaberration of the objective lens in Example 12 up to numerical aperture0.45 and numerical aperture 0.65, for wavelength λ=780 nm. FIGS. 85–87show diagrams of spherical aberration of the objective lens in Example12 respectively for λ=650 nm, λ=400 nm and λ=780 nm.

Lens data of Example 12 will be shown as follows.

Example 12

$\begin{matrix}{f = {{3.31\mspace{14mu}\begin{matrix}{{Image}\mspace{14mu}{side}} \\{{NA}\mspace{14mu} 0.65}\end{matrix}\mspace{14mu}{Magnification}}\mspace{14mu} - {0.203\mspace{14mu}\begin{matrix}\begin{matrix}\left( {for} \right. \\{wavelength}\end{matrix} \\\left. {\lambda = {650\mspace{14mu}{nm}}} \right)\end{matrix}}}} \\{f = {{3.14\mspace{14mu}\begin{matrix}{{Image}\mspace{14mu}{side}} \\{{NA}\mspace{14mu} 0.65}\end{matrix}\mspace{14mu}{Magnification}}\mspace{14mu} - {0.190\mspace{14mu}\begin{matrix}\begin{matrix}\left( {for} \right. \\{wavelength}\end{matrix} \\\left. {\lambda = {400\mspace{14mu}{nm}}} \right)\end{matrix}}}} \\{f = {{3.34\begin{matrix}{{Image}\mspace{14mu}{side}} \\{{NA}\mspace{14mu} 0.65} \\\left( {{NA}\mspace{14mu} 0.65} \right)\end{matrix}\mspace{14mu}{Magnification}}\mspace{14mu} - {0.205\mspace{14mu}\begin{matrix}\begin{matrix}\left( {for} \right. \\{wavelength}\end{matrix} \\\left. {\lambda = {780\mspace{14mu}{nm}}} \right)\end{matrix}}}}\end{matrix}$

TABLE 12 n n n (λ = (λ = (λ = Surface No. r d 650 nm) 400 nm) 780 nm)Light source ∞ 20.0 Aperture ∞ 0.0 2 (Aspheric 2.450359 2.2 1.877071.92261 1.86890   surface 1   Diffraction   surface 1) 3 (Aspheric9.108348 1.4503   surface 2   Diffraction   surface 2) 4 ∞ d4 1.580301.62441 1.57346 5 ∞ d5 Image point ∞ for λ = 650 nm for λ = 400 nm for λ= 780 nm d4 0.6 0.6 1.2 d4 0.7500 0.5540 0.4097 Aspheric surface 1 κ =−0.08796008 A4 = −0.010351744 A6 = 0.0015514472 A8 = −0.00043894535 A10= 5.481801 × 10⁻⁵ A12 = −4.2588508 × 10⁻⁶ Diffraction surface 1 B2 = 0B4 = −61.351934 B6 = 5.9668445 B8 = −1.2923244 B10 = 0.041773541Aspheric surface 2 κ = −302.6352 A4 = 0.002 A6 = −0.0014 A8 = 0.0042 A10= −0.0022 A12 = 0.0004 Diffraction surface 2 B2 = 0 B4 = 341.19136 B6 =−124.16233 B8 = 49.877242 B10 = −5.9599182

In an optical pickup apparatus having therein an objective lens likethat in Example 12 and three light sources, it is possible to correctspherical aberration caused by the difference of transparent substratethickness and chromatic aberration of spherical aberration caused by thedifference of wavelength, for each disk. As is clear from FIG. 84, anoutside of the numerical aperture NA 0.45 in practical use is made to beflare on the third optical disk.

Example 13

An objective lens of Example 13 is another concrete example of anobjective lens related to the fourth embodiment, and is structured sothat collimated light from an infinite distance may enter the objectivelens. In this example, the square terms and terms other than the squareterm are used as coefficients of the phase difference function of thediffraction surface.

FIGS. 88–90 show diagrams for the optical path of the objective lens inExample 13 respectively for λ=650 nm. λ=400 nm and λ=780 nm. FIG. 91 andFIG. 92 show the diagrams of spherical aberration of the objective lensin Example 13 up to numerical aperture 0.60, respectively for λ=650 nmand λ=400 nm. FIG. 93 and FIG. 94 show the diagrams of sphericalaberration of the objective lens in Example 13 up to numerical aperture0.45 and numerical aperture 0.60, for wavelength λ=780 nm. FIGS. 95–97show diagrams of spherical aberration of the objective lens in Example13 respectively for λ=650 nm, =400 nm and λ=780 nm.

Lens data of Example 13 will be shown as follows.

Example 13

-   f=3.31 Image side NA 0.60 (for wavelength λ=650 nm)-   f=3.14 Image side NA 0.60 (for wavelength λ=400 nm)-   f=3.34 Image side NA 0.45 (for wavelength λ=780 nm) (NA 0.60)

TABLE 13 n n n (λ = (λ = (λ = Surface No. r d 650 nm) 400 nm) 780 nm)Aperture ∞ 0.0 2 (Aspheric 2.016831 2.2 1.53771 1.55765 1.53388  surface 1   Diffraction   surface 1) 3 (Aspheric −12.04304 0.7555  surface 2   Diffraction   surface 2) 4 ∞ d4 1.58030 1.62441 1.57346 5∞ d5 Image point ∞ for λ = 650 nm for λ = 400 nm for λ = 780 nm d4 0.60.6 1.2 d4 0.7500 0.7500 0.3409 Aspheric surface 1 κ = −0.3363369 A4 =−0.0025421455 A6 = −0.0010660122 A8 = 4.7189743 × 10⁻⁵ A10 = 1.5406396 ×10⁻⁶ A12 = −7.0004876 × 10⁻⁶ Diffraction surface 1 B2 = −177.66083 B4 =−46.296284 B6 = −6.8014831 B8 = 1.6606499 B10 = −0.39075825 Asphericsurface 2 κ = 43.44262 A4 = 0.002 A6 = −0.0014 A8 = 0.0042 A10 = −0.0022A12 = 0.0004 Diffraction surface 2 B2 = 241.52445 B4 = 402.41974 B6 =−191.87213 B8 = 64.779696 B10 = −8.6741764

In the present example, it is possible to correct spherical aberrationcaused by the difference of thickness of the transparent substrate andto correct chromatic aberration of spherical aberration and axialchromatic aberration both caused by the difference of wavelength, foreach disk, because square terms and terms other than the square termsare used as coefficients of the phase difference function of thediffraction surface. As is clear from FIG. 94, an outside of thenumerical aperture NA 0.45 in practical use is made to be flare on thethird optical disk.

Example 14

An objective lens of Example 14 is a concrete example of an objectivelens related to the sixth embodiment, and is structured so thatcollimated light with wavelengths of 400 nm and 650 nm from an infinitedistance and diverged light with wavelength of 780 nm may enter theobjective lens. In this example, square terms and terms other than thesquare terms are used as coefficients of the phase difference functionof the diffraction surface.

FIG. 98 shows a diagram for the optical path of the objective lens inExample 14 for λ=400 nm. FIGS. 99–101 show the diagrams of sphericalaberration of the objective lens in Example 14 up to numerical aperture0.65, respectively for λ=400 nm±10 nm, =650 nm±10 nm and =780 nm±10 nm.

Lens data of Example 14 will be shown as follows.

Example 14

-   f=Image side NA 0.65 (for wavelength λ=650 nm)-   f=Image side NA 0.65 (for wavelength λ=400 nm)-   f=Image side NA 0.45 (for wavelength λ=780 nm) (NA 0.65)

TABLE 14 n n n (λ = Surface No. r d (λ = 650 nm) (λ = 400 nm) 780 nm)Light source ∞ d0 Aperture ∞ 0 2 (Aspheric 2.15759 2.400 1.561 1.5411.537 surface 1 Diffraction surface) 3 (Aspheric 0.976 surface 2) 4 ∞ d41.622 1.578 1.571 5 ∞ d5 Image point ∞ for λ = 400 nm for λ = 650 nm forλ = 780 nm d0 ∞ ∞ 75.17 d4 0.6 0.6 1.2 d5 0.649 0.733 0.532 Focaldistance 3.33 3.44 3.46 Aspheric surface 1 κ = −2.0080 A4 = 0.18168 × 10− 1 A6 = −0.91791 × 10 − 3 A8 = 0.16455 × 10 − 3 A10 = −0.11115 × 10 − 4Diffraction surface b2 = −0.51589 × 10 − 3 b4 = −0.24502 × 10 − 3 b6 =0.49557 × 10 − 4 b8 = −0.14497 × 10 − 4 Aspheric surface 2 κ = 3.1831 A4= 0.14442 × 10 − 1 A6 = −0.17506 × 10 − 2 A8 = 0.21593 × 10 − 4 A10 =0.12534 × 10 − 4

Incidentally, the invention is not limited to the examples explainedabove. Though the diffraction surface is formed on each of both sides ofthe objective lens, it may also be provided on a certain surface of anoptical element in an optical system of the optical pickup apparatus.Further, though the ring-zonal diffraction surface is formed on theentire surface of the lens, it may also be formed partially. Inaddition, though optical design has been advanced under the assumptionthat a light source wavelength is 400 nm and a thickness of atransparent substrate is 0.6 mm, for the target of an advanced highdensity optical disk employing blue laser, the invention can also beapplied to the optical disk with specifications other than the aforesaidspecifications.

Next, the seventh embodiment of the invention will be explained asfollows.

FIG. 117 shows a schematic structure of an objective lens and an opticalpickup apparatus including the objective lens in the present embodiment.As is shown in FIG. 117, first semiconductor laser 111 and secondsemiconductor laser 112 are unitized as a light source. Betweencollimator 13 and objective lens 16, there is arranged beam splitter 120through which a beam collimated mostly by the collimator 13 passes toadvance to the objective lens 16. Further, the beam splitter 120 servingas an optical path changing means changes an optical path of a lightflux reflected on information recording surface 22 so that the lightflux may advance to optical detector 30. The objective lens 16 has onits peripheral portion flange section 16 a which makes it easy to mountthe objective lens 16 on the optical pickup apparatus. Further, sincethe flange section 16 a has its surface extending in the direction whichis almost perpendicular to an optical axis of the objective lens 16, itis possible to mount the objective lens more accurately.

When reproducing the first optical disk, a light flux emitted from thefirst semiconductor laser 111 passes through collimator 13 to become acollimated light flux which further passes through beam splitter 120 tobe stopped down by aperture 17, and is converged by objective lens 16 oninformation recording surface 22 through transparent substrate 21 of thefirst optical disk 20. Then, the light flux modulated by informationbits and reflected on the information recording surface 22 is reflectedon beam splitter 120 through aperture 17, then, is given astigmatism bycylindrical lens 180, and enters optical detector 30 through concavelens 50. Thereby, signals outputted from the optical detector 30 areused to obtain reading signals of information recorded on the firstoptical disk 20.

Further, a change in quantity of light caused by a change in shape andposition of a spot on the optical detector 30 is detected to detect afocused point and a track. Based on this detection, objective lens 16 ismoved so that a light flux from the first semiconductor laser 111 may becaused by two-dimensional actuator 150 to form an image on informationrecording surface 22 on the first optical disk 20, and objective lens 16is moved so that a light flux from the first semiconductor laser 111 mayform an image on a prescribed track.

When reproducing the second optical disk, a light flux emitted from thesecond semiconductor laser 112 passes through collimator 13 to become acollimated light flux which further passes through beam splitter 120 tobe stopped down by aperture 17, and is converged by objective lens 16 oninformation recording surface 22 through transparent substrate 21 of thesecond optical disk 20. Then, the light flux modulated by informationbits and reflected on the information recording surface 22 is reflectedon beam splitter 120 through aperture 17, then, is given astigmatism bycylindrical lens 180, and enters optical detector 30 through concavelens 50. Thereby, signals outputted from the optical detector 30 areused to obtain reading signals of information recorded on the secondoptical disk 20. Further, a change in quantity of light caused by achange in shape and position of a spot on the optical detector 30 isdetected to detect a focused point and a track. Based on this detection,objective lens 16 is moved so that a light flux from the firstsemiconductor laser 112 may be caused by two-dimensional actuator 15 toform an image on information recording surface 22 on the second opticaldisk 20, and objective lens 16 is moved so that a light flux from thesecond semiconductor laser 112 may form an image on a prescribed track.

Objective lens (diffraction lens) 16 is designed so that its wave-frontaberration may be 0.07 λrms or less for each wavelength (λ) for incidentlight from each semiconductor laser, up to the numerical aperture(maximum numerical aperture which is greater than those necessary forrecording and/or reproducing of the first and second optical disks.Therefore, the wave-front aberration on the image forming surface ofeach light flux is 0.07 λrms or less. Accordingly, no flare is caused onan image forming surface and on the detector 30 when recording and/orreproducing either disk, resulting in better characteristics forfocusing error detection and track error detection.

Incidentally, there are assumed a case wherein the first optical disk isDVD (light source wavelength 650 nm) and the second optical disk is CD(light source wavelength 780 nm), and a case wherein the first opticaldisk is an advanced high density disk (light source wavelength 400 nm)and the second optical disk is DVD (light source wavelength 650 nm). Inparticular, when there is a big difference between necessary numericalapertures of both optical disks like the aforesaid occasion, a spot issometimes too small compared with a necessary spot diameter. In thiscase, an aperture regulating means explained in other places in thisdocument can be introduced to obtain the desired spot diameter.

Examples 15, 16, 17 and 18 for spherical-aberration-corrected lens willbe explained as follows, as a concrete example of an objective lensrelated to the seventh embodiment. In each example, the wave-frontaberration is corrected to be 0.07 λrms or less for the maximumnumerical aperture. Incidentally, the image side mentioned in thefollowing explanation means the optical information recording mediumside.

Example 15

FIG. 118 shows a diagram of an optical path of a diffraction opticallens (objective lens having a diffraction surface) representing theobjective lens in Example 15. FIG. 119 shows a spherical aberrationdiagram up to numerical aperture 0.60 for wavelengths (λ)=640, 650 and660 nm concerning the diffraction optical lens of Example 15. FIG. 120shows a diagram of an optical path of the diffraction optical lens ofthe Example 15 wherein the thickness of the transparent substrate of theoptical information recording medium is greater than that in FIG. 118.FIG. 121 shows diagrams of spherical aberration up to numerical aperture0.60 for wavelengths λ=770, 780 and 790 nm concerning the diffractionoptical lens in the case of FIG. 120.

According to the diffraction optical lens of Example 15, all aperturesup to NA 0.60 are almost no-aberration for wavelength λ=650 nm as shownin FIG. 119. As shown in FIGS. 120 and 121 where the transparentsubstrate is thick, all apertures up to NA 0.60 are almost no-aberrationfor wavelength λ=780 nm. Incidentally, a prescribed numerical aperturefor λ=780 nm is 0.45.

As stated above, in the Example 15, the spherical aberration in the caseof wavelength 780 nm where the transparent substrate of the opticalinformation recording medium is thicker than that in Examples 1, 6 and 8can be corrected up to the numerical aperture (NA 0.60) which is thesame as that in the case where the transparent substrate is thinner andwavelength is 650 nm.

Lens data in Example 15 will be shown as follows.For wavelength λ=650 nm,Focal distance f=3.33 Numerical aperture on the image side NA=0.60Infinite specification (incident collimated light flux)(0453For wavelength λ=780 μm,Focal distance f=3.38 Numerical aperture on the image side NA=0.60Infinite specification

TABLE 15 Surface No. R d n(λ = 650 nm) n(λ = 780 nm) OBJ InfinityInfinity STO Infinity 0.0 2 (Aspheric 2.06085 2.2 1.54113 1.53728surface 1 Diffraction surface) 3 (Aspheric −6.98986 1.059 surface 2) 4Infinity d4 1.57787 1.57084 5 Infinity d5 d4 d5 For λ = 650 nm 0.6 0.700For λ = 780 nm 1.2 0.364 Aspheric surface coefficient Aspheric surface 1K = −1.0358 A₄ = 4.8632 × 10⁻³ A₆ = 5.3832 × 10⁻⁴ A₆ = −1.5773 × 10⁻⁴A₁₀ = 3.8683 × 10⁻⁷ Aspheric surface 2 K = −9.256352 A₄ = 1.5887 × 10⁻²A₆ = −5.97422 × 10⁻³ A₆ = 1.11613 × 10⁻³ A₁₀ = −9.39682 × 10⁻⁵Diffraction surface coefficient(Standard wavelength 650 nm) b₂ = 6.000 ×10⁻³ b₄ = −1.317 × 10⁻³ b₆ = 1.5274 × 10⁻⁴ b₈ = −6.5757 × 10⁻⁵ b₁₀ =6.2211 × 10⁻⁶

Example 16

FIG. 122 shows a diagram of an optical path of a diffraction opticallens (objective lens having a diffraction surface) representing theobjective lens in Example 16. FIG. 123 shows a spherical aberrationdiagram up to numerical aperture 0.60 for wavelengths (λ)=640, 650 and660 nm concerning the diffraction optical lens of Example 16. FIG. 124shows a diagram of an optical path of the diffraction optical lens ofthe Example 16 wherein the thickness of the transparent substrate of theoptical information recording medium is greater than that in FIG. 122.FIG. 125 shows diagrams of spherical aberration up to numerical aperture0.60 for wavelengths λ=770, 780 and 790 nm concerning the diffractionoptical lens in the case of FIG. 124.

According to the diffraction optical lens of Example 16, all aperturesup to NA 0.60 are almost no-aberration for wavelength λ=650 nm as shownin FIG. 123. As shown in FIGS. 124 and 125 where the transparentsubstrate is thick, all apertures up to NA 0.60 are almost no-aberrationfor wavelength λ=780 nm. Incidentally, a prescribed numerical aperturefor λ=780 nm is 0.45.

As stated above, in the Example 16, the spherical aberration in the caseof wavelength 780 nm where the transparent substrate of the opticalinformation recording medium is thicker than that in Examples 1, 6 and 8can be corrected up to the numerical aperture (NA 0.60) which is thesame as that in the case where the transparent substrate is thinner andwavelength is 650 nm. Incidentally, in Examples 15 and 16, a powerfulcorrecting action for spherical aberration caused by diffraction isnecessary for correcting spherical aberration caused by a difference intransparent substrate thickness up to NA 0.6. For this reason, aring-zonal pitch is reduced, but the reduction of the pitch is relievedby making the paraxial power of diffraction to be negative.

Lens data in Example 16 will be shown as follows.For wavelength λ=650 nm,Focal distance f=3.33 Numerical aperture on the image side NA=0.60Infinite specification(0463For wavelength λ=780 nm,Focal distance f=3.36 Numerical aperture on the image side NA=0.60Infinite specification

TABLE 16 Surface No. R d n(λ = 650 nm) n(λ = 780 nm) OBJ InfinityInfinity STO Infinity 0.0 2 (Aspheric 2.09216 2.200 1.54113 1.53728surface 1 Diffraction surface) 3 (Aspheric −7.49521 1.024 surface 2) 4Infinity d4 1.57787 1.57084 5 Infinity d5 d4 d5 For λ = 650 nm 0.6 0.699For λ = 780 nm 1.2 0.345 Aspheric surface coefficient Aspheric surface 1K = −1.1331 A₄ = 4.5375 × 10⁻³ A₆ = 1.2964 × 10⁻³ A₆ = −3.6164 × 10⁻⁴A₁₀ = 2.0765 × 10⁻⁵ Aspheric surface 2 K = −4.356298 A₄ = 1.57427 × 10⁻²A₆ = −4.91198 × 10⁻³ A₆ = 7.72605 × 10⁻⁴ A₁₀ = −5.75456 × 10⁻⁵Diffraction surface coefficient (Standard wavelength 650 nm) b₂ = 2.1665× 10⁻³ b₄ = −2.0272 × 10⁻³ b₆ = 5.5178 × 10⁻⁴ b₈ = −1.8391 × 10⁻⁴ b₁₀ =1.8148 × 10⁻⁵

Example 17

FIG. 126 shows a diagram of an optical path of a diffraction opticallens (objective lens having a diffraction surface) representing theobjective lens in Example 17. FIG. 127 shows a spherical aberrationdiagram up to numerical aperture 0.60 for wavelengths (λ)=640, 650 and660 nm concerning the diffraction optical lens of Example 17. FIG. 128shows a diagram of an optical path of the diffraction optical lens ofthe Example 17 wherein the thickness of the transparent substrate of theoptical information recording medium is greater than that in FIG. 126.FIG. 129 shows diagrams of spherical aberration up to numerical aperture0.60 for wavelengths λ=770, 780 and 790 nm concerning the diffractionoptical lens in the case of FIG. 128.

According to the diffraction optical lens of Example 17, all aperturesup to NA 0.60 are almost no-aberration for wavelength λ=650 nm as shownin FIG. 127. As shown in FIGS. 128 and 129 where the transparentsubstrate is thick, all apertures up to NA 0.60 are almost no-aberrationfor wavelength λ=780 nm. Incidentally, a prescribed numerical aperturefor λ=780 nm is 0.45. Axial chromatic aberration in each of Examples15–17 is different from others, and a ring-zonal pitch is also differentfrom others.

As stated above, in the Example 17, the spherical aberration in the caseof wavelength 780 nm where the transparent substrate of the opticalinformation recording medium is thicker than that in Examples 1, 6 and 8can be corrected up to the numerical aperture (NA 0.60) which is thesame as that in the case where the transparent substrate is thinner andwavelength is 650 nm.

Lens data in Example 17 will be shown as follows.

For wavelength λ=650 nm,

Focal distance f=3.33 Numerical aperture on the image side NA=0.60Infinite specificationFor wavelength λ=780 nm,Focal distance f=3.34 Numerical aperture on the image side NA=0.60Infinite specification

TABLE 17 Surface No. R d n(λ = 650 nm) n(λ = 650 nm) OBJ InfinityInfinity STO Infinity 2 (Aspheric 2.14757 2.200 1.54113 1.53728 surface1 Diffraction surface) 3 (Aspheric −7.74682 1.0333 surface 2) 4 Infinityd4 1.57787 1.57084 5 Infinity d5 d4 d5 For λ = 650 nm 0.6 0.700 For λ =780 nm 1.2 0.327 Aspheric surface coefficient Aspheric surface 1 K =−1.0751 A₄ = 5.0732 × 10⁻³ A₆ = 4.3722 × 10⁻⁴ A₈ = −1.4774 × 10⁻⁴ A₁₀ =9.6694 × 10⁻⁷ Aspheric surface 2 K = −10.41411 A₄ = 1.59463 × 10⁻² A₆ =−6.02963 × 10⁻³ A₈ = 1.11268 × 10⁻³ A₁₀ = −9.3151 × 10⁻⁵ Diffractionsurface coefficient (Standard wavelength 650 nm) b₂ = −2.000 × 10⁻³ b₄ =−1.4462 × 10⁻³ b₆ = 1.1331 × 10⁻⁴ b₈ = −6.6211 × 10⁻⁵ b₁₀ = 6.8220 ×10⁻⁶

Example 18

FIG. 130 shows a diagram of an optical path of a diffraction opticallens (objective lens having a diffraction surface) representing theobjective lens in Example 18. FIG. 131 shows a spherical aberrationdiagram up to numerical aperture 0.70 for wavelengths (λ)=390, 400 and410 nm concerning the diffraction optical lens of Example 18. FIG. 132shows a diagram of an optical path of the diffraction optical lens ofthe Example 18 wherein the thickness of the transparent substrate of theoptical information recording medium is greater than that in FIG. 130.FIG. 133 shows diagrams of spherical aberration up to numerical aperture0.70 for wavelengths λ=640, 650 and 660 nm concerning the diffractionoptical lens in the case of FIG. 132.

According to the diffraction optical lens of Example 18, all aperturesup to NA 0.70 are almost no-aberration for wavelength λ=400 nm as shownin FIG. 131. As shown in FIGS. 132 and 133 where the transparentsubstrate is thick, all apertures up to NA 0.70 are almost no-aberrationfor wavelength λ=650 nm.

As stated above, in the Example 17, the spherical aberration in the caseof wavelength 650 nm where the transparent substrate of the opticalinformation recording medium is thicker than that in Examples 1, 6 and 8can be corrected up to the numerical aperture (NA 0.70) which is thesame as that in the case where the transparent substrate is thinner andwavelength is 400 nm.

Lens data in Example 18 will be shown as follows.For wavelength λ=400 nm,Focal distance f=3.33 Numerical aperture on the image side NA=0.70Infinite specificationFor wavelength λ=650 nm,Focal distance f=3.43 Numerical aperture on the image side NA=0.70Infinite specification

TABLE 18 Surface No. R d n(λ = 650 nm) n(λ = 650 nm) OBJ InfinityInfinity STO Infinity 2 (Aspheric 2.65858 2.40 1.71657 1.68987 surface 1Diffraction surface) 3 (Aspheric −15.86969 1.297 surface 2) 4 Infinityd4 1.62158 1.57787 5 Infinity d5 d4 d5 For λ = 650 nm 0.1 0.704 For λ =780 nm 0.6 0.469 Aspheric surface coefficient Aspheric surface 1 K = 0.0A₄ = −7.9616 × 10⁻⁴ A₆ = −5.7265 × 10⁻⁴ A₈ = 8.3209 × 10⁻⁵ A₁₀ = −4.1599× 10⁻⁵ Aspheric surface 2 K = 0.0 A₄ = 3.11131 × 10⁻² A₆ = −1.18548 ×10⁻² A₈= 1.63937 × 10⁻³ A₁₀ = −6.60514 × 10⁻⁵ Diffraction surfacecoefficient (Standard wavelength 400 nm) b₂ = −1.4046 × 10⁻³ b₄ =−8.6959 × 10⁻⁴ b₆ = 2.3488 × 10⁻⁴ b₈ = −5.2455 × 10⁻⁵ b₁₀ = 3.6385 ×10⁻⁶

Next, a pitch of plural annular bands of a diffraction optical lens ineach of the Examples 1–3 and Examples 14–18 will be explained. Each ofthe plural annular bands is formed to be almost in a form of aconcentric circle whose center is an optical axis, and values of pitchPf (mm) of the annular band corresponding to the maximum numericalaperture of the lens on the image side, pitch Pf (mm) of the annularband corresponding to the numerical aperture representing a half of themaximum numerical aperture, and ((Ph/Pf)−2) are shown in Table 19.

TABLE 19 Example Pf Ph Ph/Pf − 2 1 0.009 0.110 10.2 2 0.067 0.255 1.8 30.012 0.032 0.67 14 0.039 0.221 3.7 15 0.027 0.091 1.4 16 0.014 0.35323.2 17 0.010 0.065 4.5 18 0.011 0.060 3.50.4≦|(Ph/Pf)−2|<25  (b1)

According to the further study of the inventors of the presentinvention, it has been found that when the aforesaid expression (b1)holds, namely, when the value of |(Ph/Pf)−2| is not less than the lowerlimit of the expression, the diffraction action to correct sphericalaberration of a high ordered is not attenuated, and therefore, adifference of spherical aberration between two wavelengths caused by adifference of thickness of transparent substrates can be corrected bythe diffraction action, while, when the aforesaid value is not more thanthe upper limit, a portion where the pitch of diffraction annular bandsis too small is hardly caused, and it is possible to manufacture a lenshaving high diffraction efficiency.

With regard to the aforesaid relational expression, the followingexpression (b2) is preferable, and expression (b3) is more preferable.0.8≦|(Ph/Pf)−2|≦6.0  (b2)1.2≦|(Ph/Pf)−2|≦2.0  (b3)

Next, 8th Embodiment of the invention will be explained.

Necessary numerical aperture NA1 of the objective lens on the opticalinformation recording medium side which is needed for recording andreproducing DVD by the use of a light source having wavelength of 650 nmis about 0.6, and necessary numerical aperture NA2 of the objective lenson the optical information recording medium side which is needed forreproducing CD by the use of a light source having wavelength of 780 nmis about 0.45 (0.5 for recording). Therefore, the diffraction patternfor the correction of aberration stated above is not indispensable, upto numerical aperture NA1.

Further, the diffraction pattern is not indispensable in the vicinity ofan optical axis, because a depth of focus is great and an amount ofspherical aberration is small.

By forming a diffraction pattern on a necessary and least portion and bymaking the residual portion to be a refraction surface, it is possibleto prevent damage of a tool in the course of metal mold processing, toimprove releasing property, and to prevent deterioration of capacitywhich is caused when there is a thickness difference in disks caused bythat a light-converging spot is narrowed down more than necessary on theCD side, or is caused when a disk is inclined.

For this purpose, the diffraction pattern of the objective lens needs tobe rotation-symmetrical about an optical axis, and the followingconditions need to be satisfied, when + primary diffracted ray comingfrom the circumference of a circle of the diffraction pattern on theobjective lens farthest from the optical axis for the light flux emittedfrom the first light source is converted into a light flux withnumerical aperture NAH1 on the optical information recording mediumside, and when + primary diffracted ray coming from the circumference ofa circle of the diffraction pattern on the objective lens closest to theoptical axis for the light flux emitted from the first light source isconverted into a light flux with numerical aperture NAL1 on the opticalinformation recording medium side.NAH1<NA10≦NAL1≦NA2

When the first optical information recording medium is DVD, wavelengthλ1 of the first light source is 650 nm, the second optical informationrecording medium is CD and wavelength λ2 of the second light source is780 nm, it is preferable that NAH1 is from 0.43 to 0.55 and NAL1 is from0.10 to 0.40.

An optical design of an objective lens concerning the portion having adiffraction pattern is conducted so that + primary diffracted ray of alight flux entering the objective lens from the first light source maybe a light-converging spot which is almost no-aberration. On the otherhand, an optical design of an objective lens concerning the portionhaving no diffraction pattern is conducted so that a light flux enteringthe objective lens from the first light source may be a light-convergingspot which is almost no-aberration.

Light-converging positions for both of them stated above need to agreemostly. Further, it is important that a phase of each light flux agreeswith others. Incidentally, with regard to the phase, when k represents asmall integer, light-converging characteristic under the designedwavelength is hardly changed despite deviation of 2 kπ, but when anabsolute value of |k| is great, the light-converging characteristic iseasily changed by the wavelength fluctuation. It is preferable that |k|is in a range of 1–10.

Among light fluxes emitted from the second light source, in this case, +primary diffracted ray from the circumference of a circle of diffractionpattern on the objective lens which is farthest from an optical axis isconverted into a light flux whose numerical aperture on the opticalinformation recording medium side is NAH2, and concurrently with this, +primary diffracted ray from the circumference of a circle of thediffraction pattern which is closest to an optical axis is convertedinto a light flux whose numerical aperture on the optical informationrecording medium side is NAL2.

Spherical aberration of a light flux passing through an objective lensis established, so that a light-converging position and a phasedifference for each of a light flux from a portion having a diffractionpattern and a light flux from a portion having no diffraction patternmay be optimum, and thereby, a spot making recording and reproduction ofthe second optical information recording medium possible may be formedon an information recording surface of the optical information recordingmedium by the use of a light flux whose numerical aperture through anobjective lens is NAH2 or less, among light fluxes emitted from thesecond light source.

In practice, it is preferable that wave-front aberration at a best imagepoint through a transparent substrate of the first optical informationrecording medium for a light flux whose numerical aperture through anobjective lens is NA1 or less among light fluxes emitted from the firstlight source is 0.07 λrms or less, and wave-front aberration at a bestimage point through a transparent substrate of the second opticalinformation recording medium for a light flux whose numerical aperturethrough an objective lens is NAH2 or less among light fluxes emittedfrom the second light source is 0.07 λrms or less.

Incidentally, in particular, it is preferable that a sphericalaberration component of wave-front aberration at a best image pointthrough a transparent substrate of the first optical informationrecording medium for a light flux whose numerical aperture through anobjective lens is NA1 or less among light fluxes emitted from the firstlight source is 0.05 λrms or less.

When an optical pickup apparatus is made to be one wherein at least onecollimator is provided between the first light source and an objectivelens and between the second light source and an objective lens, andthereby, each of a light flux entering the objective lens from the firstlight source and a light flux entering the objective lens from thesecond light source is collimated light, adjustment of a pickup is easy.

Further, it is possible to reduce cost of an optical pickup apparatus byusing one collimator for both light fluxes emitted respectively from thefirst light source and the second light source.

Incidentally, when each of the first light source and the second lightsource is in a separate package, a position of each light source can beset for the collimator so that each light flux may be in parallel witheach other.

When the first light source and the second light source are in the samepackage, it is also possible to make each incident light to an objectivelens to be in parallel with each other by setting the difference betweenpositions of both light sources in the optical direction to beappropriate, or it is also possible, when adjustment is impossible, tomake each incident light to an objective lens to be in parallel witheach other by using one wherein chromatic aberration of a collimator ismade to be optimum.

In addition, a light flux entering an objective lens may be either aconverged light flux or a diverged light flux, and by making the lightflux entering an objective lens from the second light source to behigher in terms of divergence than that entering an objective lens fromthe first light source, there is generated under spherical aberrationcaused by the difference of divergence, which can reduce an amount ofspherical aberration corrected by diffraction pattern.

FIG. 114 is an illustration wherein numerical aperture NAH2 is the sameas numerical aperture NAL2, and spherical aberration of the light fluxpassing through a transparent substrate of the second opticalinformation recording medium (CD) is shown for the light flux emittedfrom the second light source, for the occasion where paraxial chromaticaberration is not corrected and the occasion where paraxial chromaticaberration is corrected (ΔfB=0).

A converged position of a light flux contributing to reproduction of thesecond optical information recording medium having NAH2 or less is atpoint B when it is not corrected by a diffraction pattern, and it isconverged to point A after being corrected by diffraction pattern tocause ΔfB to be almost 0. However, outside the NAH2, no correction ismade by the diffraction pattern, and its aberration shows aberrationcurve S by the refraction surface only.

As is apparent from the diagram, the gap between the converging point ofa light flux and spherical aberration in NAH2 grows greater bycorrection amount ΔfB of paraxial chromatic aberration, and a positionwhere a flare component from NAH2 to NA1 is converged is away greatlyfrom the converging position of the light flux contributing toreproduction of the second optical information recording medium for NAH2or less. Therefore, an influence of the flare component is small on theoptical detector.

Further, by correcting paraxial chromatic aberration at λ1 and λ2,paraxial chromatic aberration is small even in the vicinity of λ1 andλ2, and even when oscillated wavelength is varied by fluctuation oflaser power in the course of recording information on an opticalinformation recording medium, shift of focus is hardly caused, and highspeed recording is possible.

To make a position where a flare component from NAH2 to NA1 is convergedand the converging position of the light flux for NAH2 or less to beaway from each other, it is possible to obtain the state of correctingaberration shown in FIG. 115, by designing the second diffractionpattern so that the second diffraction pattern is arranged outside theaforesaid diffraction pattern, thereby, + primary diffracted ray of thesecond diffraction pattern is converged at the aforesaid convergingposition for a light flux from the first light source, and a lightsource from the second light source is transmitted through the seconddiffraction pattern without being diffracted by it.

Namely, FIG. 115( a) shows the state of correcting aberration for thelight flux emitted from the first light source, wherein aberrationcaused by the diffraction surface established to be relatively large ismade to be no-aberration by the correcting effect of + primarydiffracted ray for both NAH1 or more and NAH1 or less, and the lightflux is converged at the converging position. However, the light fluxpassing through the diffraction pattern outside NAH2 out of light fluxesemitted from the second light source is zero ordered light which is notsubjected to diffraction action, as shown in FIG. 115( b). Therefore, inits state of correcting aberration, aberration which is not subjected tocorrection by the diffraction pattern appears as it is. Accordingly, thegap of the spherical aberration in NAH2 grows greater, and theconverging position of the flare component is away greatly from theconverging position of the light flux contributing to reproduction ofinformation. Therefore, an influence of the flare component is small onthe optical detector.

The second diffraction pattern may also be designed so that the lightflux from the first light source may not be diffracted by the seconddiffraction pattern, and the light flux from the second light source maymainly become − primary diffracted ray. Due to this, whendiffraction-caused spherical aberration of the light flux ranging fromNAH2 to NA1 is exaggerated, spherical aberration through a transparentsubstrate of the second optical information recording medium of thelight flux whose numerical aperture through an objective lens is NAH2 orless can be corrected properly for the second light source, as shown inFIG. 113, and on the other hand, exaggerated spherical aberration of thelight flux outside NAH2 can be made to be greater. As a result, as shownin FIG. 116( b), the gap of the spherical aberration in NAH2 growsgreater, and the converging position of the flare component is awaygreatly from the converging position of the light flux contributing toreproduction of information. Therefore, an influence of the flarecomponent is small on the optical detector.

In the same way, it is possible to make an influence of flare componentsto be small, by providing in an optical path from a light source to anobjective lens an aperture regulating means which transmits a light fluxfrom the first light source and does not transmit a light flux passingthrough an area opposite to an optical axis of the first diffractionpattern out of light fluxes from the second light source, and thereby,by reducing flare components reaching an optical detector.

For the aperture regulating means, a ring-zonal filter which transmitsthe light flux from the first light source and reflects or absorbs thelight flux passing through an area opposite to an optical axis of thefirst diffraction pattern among light fluxes from the second lightsource may be arranged in the optical path after compounding an outgoinglight flux from the first light source and an outgoing light flux fromthe second light source with a light compounding means.

For the filter of this kind, it is possible to use, for example, adichroic filter employing multiple layers. It is naturally possible tomake either surface of an objective lens to have the filter effectstated above.

The aperture regulating means may also be a ring-zonal filter whichtransmits a light flux from the first light source and makes the lightflux passing through an area opposite to an optical axis of thediffraction pattern among light fluxes from the second light source tobe diffracted.

The first optical pickup apparatus—the seventh optical pickup apparatusrelating to the eighth embodiment of the invention will be explainedconcretely as follows, referring to the drawings.

The first optical pickup apparatus shown in FIG. 102 has thereinsemiconductor laser 111 representing the first light source forreproduction of the first optical disk and semiconductor laser 112 forreproduction of the second optical disk.

First, when reproducing the first optical disk, a beam is emitted fromthe first semiconductor laser 111, and the emitted beam is transmittedthrough beam splitter 190 representing a compounding means for beamsemitted from both semiconductor lasers 111 and 112, and then istransmitted through polarized beam splitter 120, collimator 130 and ¼wavelength plate 14 to become a circularly polarized and collimatedlight flux. This light flux is stopped down by aperture 170, and isconverged by objective lens 160 on information recording surface 220through transparent substrate 210 of the first optical disk 200.

The light flux modulated by information bit and reflected on theinformation recording surface 220 is transmitted again through objectivelens 160, aperture 170, ¼ wavelength plate 140 and collimator 130 toenter polarized beam splitter 120 where the light flux is reflected andis given astigmatism by cylindrical lens 18. Then, the light flux entersoptical detector 300 where signals outputted therefrom are used toobtain signals to read information recorded on the first optical disk200.

A change in quantity of light caused by changes of a form and a positionof a spot on the optical detector 300 is detected to conduct focusingdetection and track detection. Based on this detection, two-dimensionalactuator 150 moves objective lens 160 so that a light flux from thefirst semiconductor laser 111 may form an image on recording surface 220of the first optical disk 200, and moves objective lens 160 so that alight flux from the semiconductor laser 111 may form an image on aprescribed track.

When reproducing the second optical disk, a beam is emitted from thesecond semiconductor laser 112, and the emitted beam is reflected onbeam splitter 190 representing a light compounding means, and isconverged on information recording surface 220 through polarized beamsplitter 120, collimator 130, ¼ wavelength plate 140, aperture 170 andobjective lens 160, and through transparent substrate 210 of the secondoptical disk 200, in the same way as that for the light flux from thefirst semiconductor 111.

The light flux modulated by information bit and reflected on theinformation recording surface 220 enters optical detector 300 againthrough objective lens 160, aperture 170, ¼ wavelength plate 140,collimator 130, polarized beam splitter 120 and cylindrical lens 180,and signals outputted from the optical detector are used to obtainsignals to read information recorded on the second optical disk 200.

In the same way as in the case of the first optical disk, a change inquantity of light caused by changes of a form and a position of a spoton optical detector 300 is detected to conduct focusing detection andtrack detection, and two-dimensional actuator 150 moves objective lens160 for focusing and tracking.

The second optical pickup apparatus in FIG. 103 has structure which issuitable for an optical system for recording and reproduction, and anoccasion of reproduction will be explained as follows. Incidentally, inthe following example, members which are the same as those in theoptical pickup apparatus in FIG. 102 are given the same symbols.

When reproducing the first optical disk, a beam is emitted from thefirst semiconductor laser 111, and the emitted beam is reflected onpolarized beam splitter 121 and is transmitted through collimator 131and ¼ wavelength plate 141 to become circularly polarized and collimatedlight. It is further transmitted through beam splitter 190 representinga light compounding means, then, is stopped down by aperture 170, and isconverged by objective lens 160 on information recording surface 220through transparent substrate 210 of the first optical disk 200.

The light flux modulated by information bit and reflected on informationrecording surface 220 is transmitted again through beam splitter 190, ¼wavelength plate 141 and collimator 131 through objective lens 160 andaperture 170 to enter polarized beam splitter 121 where astigmatism isgiven to the light flux when it is transmitted therethrough. Then, thelight flux enters optical detector 301 where signals outputted therefromare used to obtain signals to read information recorded on the firstoptical disk 200.

A change in quantity of light caused by changes of a form and a positionof a spot on the optical detector 301 is detected to conduct focusingdetection and track detection. Based on this detection, two-dimensionalactuator 150 moves objective lens 160 so that a light flux from thefirst semiconductor laser 111 may form an image on recording surface 220of the second optical disk 200, and moves objective lens 160 so that alight flux from the semiconductor laser 111 may form an image on aprescribed track.

When reproducing the second optical disk, a beam is emitted from thesecond semiconductor laser 112, and the emitted beam is reflected onpolarized beam splitter 122 and is transmitted through collimator 132and ¼ wavelength plate 142 to become circularly polarized and collimatedlight. It is further reflected on beam splitter 190 representing a lightcompounding means, then, is converged by aperture 170 and objective lens160 on information recording surface 220 through transparent substrate210 of the second optical disk 200.

The light flux modulated by information bit and reflected on informationrecording surface 220 is reflected again on the beam splitter 190through objective lens 160 and aperture 170, and is transmitted through¼ wavelength plate 142 and collimator 132 to enter polarized beamsplitter 122 where astigmatism is given to the light flux when it istransmitted therethrough. Then, the light flux enters optical detector302 where signals outputted therefrom are used to obtain signals to readinformation recorded on the second optical disk 200.

A change in quantity of light caused by changes of a form and a positionof a spot on the optical detector 302 is detected to conduct focusingdetection and track detection. Based on this detection, two-dimensionalactuator 150 moves objective lens 160 so that a light flux from thesecond semiconductor laser 112 may form an image on recording surface220 of the first optical disk 200, and moves objective lens 160 so thata light flux from the semiconductor laser 112 may form an image on aprescribed track, which is the same as the foregoing.

The third optical pickup apparatus in FIG. 104 has structure which issuitable for an optical system for recording and reproduction, and anoccasion of reproduction will be explained as follows.

When reproducing the first optical disk, a beam is emitted from thefirst semiconductor laser 111, and the emitted beam is transmittedthrough coupling lens 60 which makes divergence of diverged lightsource, beam splitter 190 representing a light compounding means andbeam splitter 120, and is further transmitted through collimator 130 and¼ wavelength plate 140 to become circularly polarized and collimatedlight. It is further stopped down by aperture 170 and is converged byobjective lens 160 on information recording surface 220 throughtransparent substrate 210 of the first optical disk 200.

The light flux modulated by information bit and reflected on informationrecording surface 220 is transmitted again by ¼ wavelength plate 140 andcollimator 130 through objective lens 160 and aperture 170 to enter beamsplitter 120 where the light flux is reflected and is given astigmatismby cylindrical lens 180. Then, the light flux enters optical detector301 through concave lens 50, where signals outputted therefrom are usedto obtain signals to read information recorded on the first optical disk200.

A change in quantity of light caused by changes of a form and a positionof a spot on the optical detector 301 is detected to conduct focusingdetection and track detection. Based on this detection, two-dimensionalactuator 150 moves objective lens 160 so that a light flux from thefirst semiconductor laser 111 may form an image on recording surface 220of the first optical disk 200, and moves objective lens 160 so that alight flux from the semiconductor laser 111 may form an image on aprescribed track.

In the second semiconductor laser 112 for reproducing the second opticaldisk, laser/detector accumulating unit 400, optical detector 302 andhologram 230 are unitized. “Unit” or “unitization” means that unitizedmembers and means can be incorporated solidly in an optical pickupapparatus, and the unit can be incorporated as one part in assembly ofan apparatus.

The light flux emitted from the second semiconductor laser 112 istransmitted through hologram 230, then, is reflected on beam splitter190 representing a light compounding means, and is transmitted throughbeam splitter 120, collimator 130 and ¼ wavelength plate 140 to becomecollimated light. It is further converged on information recordingsurface 220 through aperture 170, objective lens 160 and throughtransparent substrate 210 of the second optical disk 200.

The light flux modulated by information bit and reflected on informationrecording surface 220 is transmitted again by ¼ wavelength plate 140 andcollimator 130 and beam splitter 120 through objective lens 160 andaperture 170, then, is reflected on beam splitter 190 and is diffractedby hologram 230 to enter optical detector 302, where signals outputtedtherefrom are used to obtain signals to read information recorded on thesecond optical disk 200.

Focusing detection and track detection are conducted by detecting achange in a quantity of light caused by the change of form and positionof a spot on optical detector 302, and thereby, objective lens 160 ismoved by two-dimensional actuator 150 for focusing and tracking.

When reproducing the first optical disk in the fourth optical pickupapparatus in FIG. 105 where laser/detector accumulating unit 410,optical detector 301 and hologram 231 are unitized to become the firstsemiconductor laser 111, the light flux emitted from the firstsemiconductor laser 111 passes through the hologram 231, and istransmitted through beam splitter 190 representing a light compoundingmeans and collimator 130 to become a collimated light flux, which isfurther stopped down by aperture 170 to be converged by objective lens160 on information recording surface 220 through transparent substrate210 of the first optical disk 200.

The light flux which is modulated by information bit and reflected oninformation recording surface 220 is transmitted by collimator 130 andbeam splitter 190 through objective lens 160 and aperture 170 again,then, is diffracted by hologram 231 to enter optical detector 301 wherethe output signals therefrom are used to obtain reading signals forinformation recorded on the first optical disk 200.

Focusing detection and track detection are conducted by detecting achange in a quantity of light caused by the change of form and positionof a spot on optical detector 302, and thereby, objective lens 160 ismoved by two-dimensional actuator 150 for focusing and tracking.

When reproducing the second optical disk where laser/detectoraccumulating unit 42, optical detector 302 and hologram 232 are unitizedto become the second semiconductor laser 112, the light flux emittedfrom the second semiconductor laser 112 passes through the hologram 232,and is reflected on beam splitter 190 and is transmitted throughcollimator 130 to become a collimated light flux, which is furtherconverged on information recording surface 220 through objective lens160 and transparent substrate 210 of the second optical disk 200.

The light flux which is modulated by information bit and reflected oninformation recording surface 220 is transmitted by collimator 130through objective lens 160 and aperture 170 and is reflected on beamsplitter 190, then, is diffracted by hologram 232 to enter opticaldetector 302 where the output signals therefrom are used to obtainreading signals for information recorded on the second optical disk 200.

Focusing detection and track detection are conducted by detecting achange in a quantity of light caused by the change of form and positionof a spot on optical detector 302, and based on this detection,objective lens 160 is moved by two-dimensional actuator 150 for focusingand tracking.

In the optical pickup apparatus in FIG. 106, the first semiconductorlaser 111, the second semiconductor laser 112, optical detector 30 andhologram 230 are unitized as laser/detector accumulated unit 430.

When reproducing the first optical disk, the light flux emitted from thefirst semiconductor laser 111 is transmitted by hologram 230 andcollimator 130 to become a collimated light flux, which is furtherstopped down by aperture 170 to be converged by objective lens 160 oninformation recording surface 220 through transparent substrate 210 ofthe first optical disk 200.

The light flux which is modulated by information bit and reflected oninformation recording surface 220 is transmitted again by collimator 130through objective lens 160 and aperture 170 and is diffracted byhologram 230 to enter optical detector 300 where the output signalstherefrom are used to obtain reading signals for information recorded onthe first optical disk 200.

Focusing detection and track detection are conducted by detecting achange in a quantity of light caused by the change of form and positionof a spot on optical detector 300, and thereby, objective lens 160 ismoved by two-dimensional actuator 150 for focusing and tracking.

When reproducing the second optical disk, the light flux emitted fromthe second semiconductor laser 112 is transmitted by hologram 230 andcollimator 130 to become mostly a collimated light flux, which isfurther converged on information recording surface 220 through objectivelens 160 and transparent substrate 210 of the second optical disk 200.

The light flux which is modulated by information bit and reflected oninformation recording surface 220 is transmitted again by collimator 130through objective lens 160 and aperture 170 and is diffracted byhologram 230 to enter optical detector 300 where the output signalstherefrom are used to obtain reading signals for information recorded onthe second optical disk 200.

Focusing detection and track detection are conducted by detecting achange in a quantity of light caused by the change of form and positionof a spot on optical detector 300, and based on this detection,objective lens 160 is moved by two-dimensional actuator 150 for focusingand tracking.

In the optical pickup apparatus in FIG. 107, the first semiconductorlaser 111, the second semiconductor laser 112, the first opticaldetector 301, the second optical detector 302 and hologram 230 areunitized as laser/detector accumulated unit 430.

When reproducing the first optical disk, the light flux emitted from thefirst semiconductor laser 111 is transmitted through the surface ofhologram 230 on the disk side and collimator 130 to become a collimatedlight flux, which is further stopped down by aperture 170 and isconverged by objective lens 160 on information recording surface 220through transparent substrate 210 of the first optical disk 200.

The light flux which is modulated by information bit and reflected oninformation recording surface 220 is transmitted again by collimator 130through objective lens 160 and aperture 170 and is diffracted by thesurface of hologram 230 on the disk side to enter optical detector 301corresponding to the first light source where the output signalstherefrom are used to obtain reading signals for information recorded onthe second optical disk 200.

Focusing detection and track detection are conducted by detecting achange in a quantity of light caused by the change of form and positionof a spot on optical detector 301, and thereby, objective lens 160 ismoved by two-dimensional actuator 150 for focusing and tracking.

When reproducing the second optical disk, the light flux emitted fromthe second semiconductor laser 112 is diffracted by the surface ofhologram 230 on the semiconductor laser side and is transmitted throughcollimator 130 to become mostly a collimated light flux. This surface ofhologram 230 on the semiconductor laser side has a function as a lightcompounding means. The light flux is converged on information recordingsurface 220 through aperture 170, objective lens 160 and transparentsubstrate 210 of the second optical disk 200.

The light flux which is modulated by information bit and reflected oninformation recording surface 220 is transmitted again by collimator 130through objective lens 160 and aperture 170 and is diffracted by thesurface of hologram 230 on the disk side to enter optical detector 302corresponding to the second light source where the output signalstherefrom are used to obtain reading signals for information recorded onthe second optical disk 200.

Focusing detection and track detection are conducted by detecting achange in a quantity of light caused by the change of form and positionof a spot on optical detector 302, and based on this detection,objective lens 160 is moved by two-dimensional actuator 150 for focusingand tracking.

The seventh optical pickup apparatus shown in FIG. 108 is of thestructure which is suitable for an optical system for recording andreproducing, and an occasion of reproduction will be explained asfollows.

When reproducing the first optical disk, the first semiconductor laser111 emits a beam which is transmitted through coupling lens 60 whichmakes divergence of a diverged light source small, beam splitter 190representing a light compounding means and beam splitter 120, and isfurther transmitted through collimator 130 and ¼ wavelength plate 140 tobecome a circularly polarized collimated light. It is further stoppeddown by aperture 170 to be converged by objective lens 160 oninformation recording surface 220 through transparent substrate 210 ofthe first optical disk 200.

The light flux modulated by information bit and reflected on informationrecording surface 220 is transmitted again by ¼ wavelength plate 140 andcollimator 130 through objective lens 160 and aperture 170 to enter beamsplitter 120 where the light flux is reflected and is given astigmatismby cylindrical lens 180. Then, the light flux enters optical detector301 through concave lens 50, and output signals therefrom are used toobtain reading signals for information recorded on the first opticaldisk 200.

Focusing detection and track detection are conducted by detecting achange in a quantity of light caused by the change of form and positionof a spot on optical detector 301. Then, based on this detection,two-dimensional actuator 150 moves objective lens 160 so that a lightflux emitted from the first semiconductor laser 111 may form an image onrecording surface 220 of the first optical disk 200, and moves objectivelens 160 so that a light flux emitted from the first semiconductor laser111 may form an image on the prescribed track.

In the second semiconductor laser 112 for reproducing the second opticaldisk, optical detector 302 and hologram 230 are unitized inlaser/detector accumulating unit 400.

The light flux emitted from the second semiconductor laser 112 istransmitted through hologram 230, then, is reflected on beam splitter190 representing a light compounding means, and is transmitted throughbeam splitter 120, collimator 130 and ¼ wavelength plate 140 to become acollimated light flux. It is further converged on information recordingsurface 220 through transparent substrate 210 of the second optical disk200 through aperture 170 and objective lens 160.

The light flux modulated by information bit and reflected on informationrecording surface 220 is transmitted again by ¼ wavelength plate 140,collimator 130 and beam splitter 120 through objective lens 160 andaperture 170, then, is reflected on beam splitter 190 and is diffractedby hologram 230 to enter optical detector 302, where output signalstherefrom are used to obtain reading signals for information recorded onthe second optical disk 200.

Focusing detection and track detection are conducted by detecting achange in a quantity of light caused by the change of form and positionof a spot on optical detector 302, and objective lens 160 is moved bytwo-dimensional actuator 150 for focusing and tracking.

There will be explained the occasion for recording and reproducing thedisk of the third Super RENS system which is mostly the same as thefirst optical disk in terms of thickness t1 of transparent substrate andof necessary numerical aperture NA of the aforesaid objective lens onthe optical information recording medium side which is needed forrecording and reproducing with the first light source having wavelengthof λ1.

The disk of the third Super RENS system is one which is now studiedintensively, and an example of its structure is shown in FIG. 109. Itsrecording and reproducing are based on near field optics, andreproduction signals include a system to use reflected light and asystem using transmitted light, and the structure of the present exampleshows a system to obtain reproduction signals by the use of transmittedlight.

When recording and reproducing the third disk of the Super RENS system,the first semiconductor laser 111 emits a beam which is transmittedthrough coupling lens 60 which makes divergence of diverged light fluxto be small, beam splitter 190 representing a light compounding meansand beam splitter 120, and is further transmitted through collimator 130and ¼ wavelength plate 140 to become a collimated light flux. It isfurther stopped down by aperture 170, and is converged by objective lens160 on non-linear optical film 250 through transparent substrate 210 ofthe first optical disk 200 and first protection film 240. On thenon-linear optical film 250, there are formed minute openings, andenergy is transmitted to information recording surface 220 on aninformation recording layer through second protection film 260. Then,the light modulated by information bit and is transmitted throughinformation recording surface 220 is transmitted through protection film270, then, is converged by converging lens 90 which is on the sideopposite to the objective lens, to reach optical detector 305, wherereading signals for information recorded on third optical disk 200 areobtained by the signals outputted from the optical detector.

On the other hand, the light flux reflected on non-linear optical film250 is transmitted again by ¼ wavelength plate 140 and collimator 130through objective lens 160 and aperture 170 to enter beam splitter 120where the light flux is reflected and is given astigmatism bycylindrical lens 180 to enter optical detector 301 through concave lens50. Focusing detection and track detection are conducted by detecting achange in a quantity of light caused by the change of form and positionof a spot on optical detector 301. Based on this detection,two-dimensional actuator 150 moves objective lens 160 so that the lightflux emitted from the first semiconductor laser 111 may form an image onnon-linear optical film 250 of the first optical disk, and movesobjective lens 160 so that the light flux emitted from the semiconductorlaser 111 may form an image on the prescribed track.

When an exclusive objective lens designed so that no-aberrationcollimated light flux may enter from the first light source and anno-aberration spot may be formed through transparent substrate of DVD isused as an objective lens of the aforesaid optical pickup apparatus, andwhen no-aberration collimated light enters the objective lens from thesecond light source and a spot is formed through a transparent substrateof CD, there is generated spherical aberration caused by

(1) wavelength-dependence of a refractive index of an objective lens,

(2) a thickness difference between transparent substrates of informationrecording media, and

(3) wavelength-dependence of a refractive index of a transparentsubstrate, and most of the spherical aberrations are caused by the aboveitem (2), which has already been stated.

The spherical aberration caused by the factor of above-mentioned item(2) is proportional mostly to |t2−t1| and to (NA2)⁴, under the conditionof numerical aperture NA2 which is necessary for recording andreproducing of CD. FIG. 110 shows relationship between image formingmagnification M2 and wave-front aberration for the exclusive lensdesigned to be no-aberration through a transparent substrate of DVD whena collimated light flux having wavelength λ1=650 nm enters an objectivelens, under the conditions that the transparent substrate is the same asCD in terms of thickness, a light source with wavelength λ2=780 nm isused, and the numerical aperture of the light flux emerging from theobjective lens is 0.45. When the image forming magnification M2 is 0, acollimated light flux enters the objective lens, which is the same asDVD.

In the case of M2=0 as illustrated, spherical aberration of about 0.13arms is generated, which is greater than 0.07 λrms which is Marechallimit of diffraction limit power. Therefore, it is necessary to setspherical aberration by some means for both DVD and CD so that thewave-front aberration may not be more than Marechal limit.

When the image forming magnification is made to be negative in thisobjective lens, negative spherical aberration is generated in theobjective lens, and it takes the minimum value within the Marechal limitin the case of M≈−0.06. As stated above, an amount of sphericalaberration which needs to be corrected varies depending on the imageforming magnification, and in the illustrated example, it is notnecessary to correct the spherical aberration with other means in thecase of M≈−0.06. Further, when NA which is necessary for informationrecording of CD-R is 0.5, the spherical aberration to be correctedfurther grows greater.

Next, there will be explained a preferable collimator adjusting means ineach optical pickup apparatus stated above. To simplify the explanation,an optical pickup apparatus employing a light converging optical systemcomposed of a collimator and an objective lens will be considered. Withregard to the distance between the collimator and a light source, whenthe light source is arranged at the focal point of the collimator on itsoptical axis, a desirable collimated light is emerged from thecollimator. Since manufacturing dispersion for the back focus of thecollimator, the distance between the mounting position of asemiconductor laser and a light-emitting point and the housing of theoptical pickup apparatus, is kept to be small, it is possible to obtaina collimated light having accuracy which is not problematic forpractical use, even when the distance between the semiconductor laserand the collimator is not adjusted.

When recording and/or reproducing two types of optical informationrecording media each having a transparent substrate with differentthickness, by the use of two light sources each having differentwavelength, and when using an objective lens having a diffractionpattern and using the diffracted ray with the same degree other thanzero for each light source, fluctuation of spherical aberration causedby variation of oscillation wavelength of the laser is greater, comparedwith a conventional double aspheric objective lens. In particular, inthe case of the objective lens in Example 6, wave-front aberration of0.001 λms at wavelength of 650 nm is deteriorated to 0.03 arms when thewavelength varies by ±10 nm. What is generated in this case is sphericalaberration. In the semiconductor laser, there is an individualdifference of oscillation wavelength, and when a semiconductor laserhaving a large individual difference is used in the optical pickupapparatus, criteria for spherical aberration of an objective lens havingdiffraction pattern become strict, which is a problem.

In an objective lens used in an optical pickup apparatus, when anincident light flux is changed from collimated light to diverged light,negative 3-ordered spherical aberration is increased, and when it ischanged from collimated light to converged light, positive 3-orderedspherical aberration is increased, thus, it is possible to control3-ordered spherical aberration by changing divergence of an incidentlight flux to the objective lens. In the objective lens as in Example 6,main components of spherical aberration caused by the individualdifference in oscillated wavelength of the semiconductor laser are3-ordered spherical aberration, thus, it is possible to make 3-orderedspherical aberration of the total light converging optical system to bethe designed value, by changing divergence of an incident light flux tothe objective lens.

Incidentally, when there is a coupling lens such as a collimator in alight converging optical system, it is possible to control the 3-orderedspherical aberration of an objective lens by moving the coupling lens inthe direction of its optical axis. Further, when there is a couplinglens such as a collimator, the same object as in the foregoing can beattained by moving a semiconductor laser in the direction of the opticalaxis. The semiconductor laser may naturally be moved in the optical axisdirection even when a coupling lens such as a collimator exists.

Example 19

As concrete examples of an objective lens related to the 8th embodiment,Example 19 of spherical-aberration-corrected lens is shown in FIG. 111,Table 20 and Table 21 as follows.

In Table 20, ri represents a radius of curvature of the refractionsurface, each of di and di′ represents a distance between surfaces, andeach of ni and ni′ represent the refractive index at main wavelength.Further, the expression for surface form is shown below.

$X = {\frac{h^{2}/r}{1 + \sqrt{1 - {\left( {1 + \kappa} \right)\left( {h/r} \right)^{2}}}} + {\sum\limits_{j}{A_{j}h^{p\; j}}}}$

In the expression, X represents an axis in the direction of the opticalaxis, h represents an axis in the direction perpendicular to the opticalaxis, the direction for advancement of light is positive, r represents aparaxial radius of curvature, κ represents constant of the cone, Ajrepresents aspheric surface coefficient, and Pj (Pi≧3) representsaspheric surface power number.

The diffraction surface is as shown in Expression 1 as a function of anoptical path difference. The unit is in mm.

TABLE 20 Wavelength 635 nm 780 nm Focal distance 3.370 3.397 Aperturediameter Φ 4.04 mm Lateral magnification of objective 0 lens Surface No.ri di di′ ni ni′ 1 ∞ 2 2.131 2.6 1.5300 1.5255 3 −6.373 1.5657 1.2052 4∞ 0.6 1.2 1.5787 1.5709 5 ∞ Both di and ni represent values for thefirst optical information recording medium (t1 = 0.6 mm). Both di′ andni′ represent values for the second optical information recording medium(t2 = 1.2 mm).

Both di and ni represent values for the first optical informationrecording medium (t1=0.6 mm).

Both di′ and ni′ represent values for the second optical informationrecording medium (t2=1.2 mm).

TABLE 21 Second First split 0 ≦ H ≦ 1.6984 surface surface κ = −3.6612 ×10⁻² (Aspheric A₁ = −3.2000 × 10⁻³ P1 = 4.0 surface A₂ = −9.5500 × 10⁻⁴P2 = 6.0 coefficient) A₃ = 9.4024 × 10⁻⁵ P3 = 8.0 A₄ = −2.8750 × 10⁻⁵ P4= 10.0 (Diffraction B₂ = 0 surface B₄ = −8.3027 × 10⁻⁴ coefficient)B_(6 = −1.6462 × 10) ⁻⁴ B₈ = 1.3105 × 10⁻⁵ Second split 1.6984 ≦ Hsurface κ = −9.8006 × 10⁻¹ (Aspheric A₁ = 6.0790 × 10⁻³ P1 = 4.0 surfaceA₂ = 2.8149 × 10⁻⁴ P2 = 6.0 coefficient) A₃ = 6.6735 × 10⁻⁶ P3 = 8.0 A₄= −2.8790 × 10⁻⁶ P4 = 10.0 Third Aspheric κ = −2.4934 × 10 surfacesurface A₁ = 9.6641 × 10⁻³ P1 = 4.0 coefficient A₂ = −3.7568 × 10⁻³ P2 =6.0 A₃ = 7.9367 × 10⁻⁴ P3 = 8.0 A₄ = −7.3523 × 10⁻⁵ P4 = 10.0

A sectional view of the lens in the aforesaid example is shown in FIG.111, and its spherical aberration diagram is shown in FIG. 112. In FIG.111, portion S2 d including an optical axis of the second surface S2 hasa diffraction pattern, and portion S2 r outside thereof is an asphericsurface refraction surface. FIG. 112( a) shows a spherical aberrationdiagram at wavelength of 635 nm and first optical information recordingmedium (t1=0.6 mm), which is sufficiently corrected in terms ofaberration. FIG. 112( b) shows a spherical aberration diagram atwavelength of 780 nm and second optical information recording medium(t2=1.2 mm), wherein a light flux passing through the first splitsurface S2 d is corrected in terms of spherical aberration by an effectof diffraction, and a light flux passing through second split surface S2r becomes flare light and has an effect which is the same as that of anaperture.

The lens in the aforesaid example is an objective lens with NAH2=0.5 andNAL2=0. The diffraction pattern section of this lens becomes a patternon a annular band whose center is an optical axis, and its step numberis about 13. A boundary between a circumferential section of thediffraction pattern which is farthest from the optical axis and therefraction surface has a step of about 21 μm.

In the case of NAH2=0.45, the number of steps of the diffraction patternis about 9, and an amount of the step is about 13 μm. An amount of thestep and the number of steps of the diffraction pattern are roughlyproportional to the fourth power of NAH2.

In the case of NAL2=0 as in the aforesaid example, the number of stepsof the diffraction pattern is increased in proportional to sphericalaberration to be corrected.

In the objective lens in the invention, satisfactory effects can beobtained even when the depth of the diffraction pattern in the directionof an optical axis is 2 μm or less. However, when the number of steps ofthe diffraction pattern is large, it is difficult to process the metalmold and to mold thus, it is desirable that the number of steps is assmall as possible.

This can be attained by the following.

(1) An image forming magnification for CD is made to be slightly smallerthan that for DVD, and an amount of spherical aberration to be correctedis made to be small in advance. It is preferable that mCD (magnificationfor recording and reproducing of CD)−mDVD (magnification for recordingand reproducing of DVD) is in a range of − 1/15–0.

(2) A diffraction pattern is not provided on the portion where the depthis great and the numerical aperture is small.

For example, if image forming magnification of DVD is made to be 0, andimage forming magnification of CD is made to be −0,03, the sphericalaberration to be corrected is halved, and even when NAH2 is made to be0.5 for covering CD-R, the number of steps is about 7 and an amount of astep is about 11 μm.

When an amount of step is small, the shape of step S2 s may also be onewhich flows smoothly from diffraction pattern section S2 d to refractionsurface section S2 r.

When image forming magnification for both DVD and CD is 0, if NAL2 ismade to be 0.36, residual spherical aberration component WSA (NAL2) ofthe wave-front aberration of a light flux whose numerical aperture isnot more than NAL2 is about 0.053 λrms. By providing the optimumdiffraction pattern to this, it is possible to make the RMS value of thewave-front aberration up to NAH2 to be small, while keeping thewave-front aberration of DVD to 0.

Residual spherical aberration component WSA (NAH2) of the wave-frontaberration of a light flux whose numerical aperture is not more thanNAH2 can be approximated by the following expression.WSA (NAH@)=(NAL2/NAH2) 2×WSA (NAL2)Therefore, the aforesaid value is 0.034 λrms for NAH2=0.45, and it is0.027 λrms for NAH2=0.5, which are sufficiently smaller than theMarechal limit value.

In this case, excessive spherical aberration is generated for NAL2 orless. Therefore, the spherical aberration from NAL2 to NAH2 is not madeto be zero, but it can be made to agree with the best focus of the lightflux of NAL2 or less. Since this best focus position is at the positionexceeding the paraxial focus point, the spherical aberration to becorrected by the diffraction pattern can be small. Further, for thelight flux for NAL2 or less, the diffraction pattern is not necessary.Due to these two effects, the number of steps of the diffraction patternin the case of NAH2=0.5 can be about 6, and the number of steps of thediffraction pattern in the case of NAH2=0.45 can be 4.

It is naturally possible to make the diffraction pattern to be smallerby making image forming magnification of CD to be smaller than that ofDVD, and the minimum of two steps makes interchangeable reproduction forDVD and CD possible.

Incidentally, there is proposed a high density optical informationrecording medium whose transparent substrate has a thickness of 0.1 mm.For recording and reproduction for this, a blue semiconductor laser isused, a two-element objective lens is used, and 0.85 is needed as NA1.On the other hand, CD-RW employs a light source wherein a thickness of atransparent substrate is 1.2 mm and a wavelength is 780, and NA2 is madeto be 0.55. In this interchangeable optical system, an amount ofcorrection of spherical aberration is 2.7 times greater, because NA2 islarge and t1−t2 is also large, compared with DVD and CD-R (NAH2=0.5).Therefore, the number of steps of the diffraction pattern is about 35.

For further correction of paraxial chromatic aberration, the number ofsteps of the diffraction pattern is increased. For the correctionincluding paraxial chromatic aberration up to NA1, hundreds of steps areneeded. In such a case, it is also possible to provide diffractionpattern to plural optical surfaces.

A certain portion within a range from NAL2 to NAH2 may also be made arefraction surface, when necessary.

Further, in the case of t1>t2, −first ordered light is used because asign of the generated spherical aberration is reversed.

Equally, even in the case of DVD and CD, image forming magnification ofan objective lens for CD is fairly smaller than that for DVD, and whenunder spherical aberration remains, −first ordered light is usedequally.

Incidentally, with regard to DVD and CD which represent a matter ofprimary concern currently, there is shown an example to execute with asingle objective lens by using two lasers each having differentrecording or wavelength. As stated already, when assuming that λ1represents a wavelength of the first light source and λ2 (λ2>λ1)represents a wavelength of the second light source, there is introducedthe first diffraction pattern wherein +first ordered diffracted ray isused in the case of t1<t2, and −first ordered diffracted ray is used inthe case of t1>t2, and the former is applied to DVD (using the firstlight source) and CD (using the second light source).

There have recently been put to practical use various light sources eachhaving a different wavelength such as a blue semiconductor laser and anSHG laser, and it is estimated that lots of new optical informationrecording media will further appear on the market. In this case, thoughthe necessary spot size is determined from the recording density of theoptical information recording medium, NA which is necessary forrecording or recording/reproduction varies dependent on a wavelength ofthe light source to be used. Therefore, each of the thickness of atransparent substrate of an optical information recording medium and ofthe necessary NA is classified into the following four cases, for twooptical information recording media.

(1) t1<t2, NA1>NA2

(2) t1<t2, NA1<NA2

(3) t1>t2, NA1>NA2

(3) t1>t2, NA1<NA2

In the aforesaid explanation, there have especially been explained indetail various items such as the number of ordered of diffraction of thefirst diffraction pattern used in the case (1) above for each lightsource, a range (NAH1, NAL1, NAH2 and NAL2), types and NA ranges of alight source wherein a diffraction pattern section and a transparentsection are required to be converged at the same position, a range of NAsetting spherical aberration for each light source, a range of NAwherein wave-front aberration for each light source is required to be0.07 λrms or less, necessity to make the number of ordered ofdiffraction of the second diffraction pattern for each light source andthe first diffraction pattern to be converged at the same position, andconditions for restricting a light flux from which light source in thecase of introducing the aperture restriction. Detailed explanation foreach of (2), (3) and (4) cases is omitted here, because they can beexecuted easily from the detailed description of (1).

For manufacturing of lenses, it is also possible either to mold plasticmaterials or glass materials solidly by the use of a metal mold in whichthe diffraction pattern is engraved, or to form, on the base material ofglass or plastic, an optical surface including the diffraction patternof the invention, by the use of UV-setting resins. It is furtherpossible to manufacture through coating or direct processing.

As stated above, it is also possible to arrange so that the opticalsurface having the effect of the invention is provided on an opticalelement which is separate from an objective lens, and the opticalsurface is provided on the side of the objective lens closer to a lightsource or on the side closer to an optical information recording medium.It can also be provided naturally on an optical surface of a collimatoror a light compounding means through which a light flux from the firstlight source and that from the second light source pass. However, anamount of tracking is restricted, because an optical axis of thediffraction pattern and that of the objective lens move relatively whenthe objective lens is moved for tracking.

Though the diffraction pattern is made to be in a form of a concentriccircle which is concentric with an optical axis, for convenience, sakeof explanation, the invention is not limited to this.

Though the objective lens shown concretely in Examples 1–19 is composedof a single lens as an example, the objective lens may also be composedof plural lenses, and an occasion wherein at least one surface of theplural lenses has the diffraction surface of the invention is includedin the invention.

In the invention, selective generation of diffracted ray with specificnumber of ordered means that diffraction efficiency of the diffractedray with the specific number of ordered is higher than that of eachdiffracted ray with number of ordered other than the specific number ofordered, for light with a prescribed wavelength, which has already beenstated. It is preferable that, for rays of light having two wavelengthswhich are different from each other, diffraction efficiency ofdiffracted ray with a specific number of ordered is higher by 10% ormore than that of each diffracted ray with another number of ordered,and it is more preferable that the efficiency is higher by 30% or more,while, the diffraction efficiency of 50% or more of the diffracted raywith the specific number of ordered is preferable, and the morepreferable is 70% or more which lessen the loss of a quantity of lightand is preferable from the viewpoint of practical use.

With regard to the diffraction surface of the invention, it ispreferable that existence of the diffraction surface improves sphericalaberration, compared with an occasion of no diffraction surface, namelyan occasion where the surface enveloping the relief of the diffractionsurface is simulated to be assumed, when diffraction rays of lightgenerated selectively and have at least two wavelengths which aredifferent from each other are focused respectively, as shown in theaforesaid embodiment and in the concrete examples of the lens.

Further, in the invention, it is preferable, from the viewpoint ofobtaining a desirable spot which is effective on a practical use, thatwave-front aberration of the diffracted ray with specific number ofordered generated selectively for each (wavelength λ) of rays of lighthaving at least two wavelengths which are different from each other is0.07 λrms.

As stated above, the invention makes it possible to obtain an opticalsystem with simple structure employing at least one optical elementhaving a diffraction surface wherein spherical aberration and axialchromatic aberration can be corrected for rays of light having at leasttwo wavelengths which are different from each other, an optical pickupapparatus, a recording and reproducing apparatus, a lens, an opticalelement, a diffraction optical system for optical disks, a recordingand/or reproducing apparatus for a sound and/or an image, and anobjective lens. It is further possible to make an optical system to besmall in size, light in weight and low in cost. When the optical elementhas a diffraction surface which makes the diffraction efficiency of thediffracted ray having the same number of ordered to be maximum for raysof light having at least two wavelengths which are different from eachother, a loss of a quantity of light can be lessened, compared with anoccasion where the diffraction efficiency of the diffracted ray of thediffraction surface having a different number of ordered is made to bemaximum.

With regard to the inventions described in Items 72–88, in particular,it is possible, by providing a diffraction lens on the diffractionsurface, to obtain a diffraction optical system wherein an opticalsystem for recording and reproducing having two light sources eachhaving a different wavelength is used, a loss of a quantity of light foreach light source wavelength is little, and aberration can be correctedup to almost the diffraction limit.

With regard to the inventions described in Items 89–98, in particular,it is possible to conduct recording of information and/or reproducing ofinformation for different optical disk with one objective lens, forthree light sources each having a different wavelength, an opticalpickup apparatus can be made thinner, and a problem of high cost can besolved, as stated above.

With regard to the inventions described in Items 99–112, in particular,it is possible to provide an optical pickup apparatus and an objectivelens wherein spherical aberration caused by a difference of thickness ofa transparent substrate, chromatic aberration of spherical aberrationgenerated by a difference of wavelength and axial chromatic aberrationare corrected, by designing an aspheric surface coefficient and acoefficient of a phase difference function properly, in an opticalpickup apparatus having three light sources each having a differentwavelength.

With regard to the inventions described in Items 113–181, in particular,it is possible to provide a spherical-aberration-corrected objectivelens for recording and reproducing an optical information recordingmedium and an optical pickup apparatus wherein recording and reproducingcan be conducted by light fluxes having different wavelengths and by asingle light converging optical system, for optical informationrecording medium having a transparent substrate with a differentthickness, by providing plural split surfaces on the objective lens andthereby by arranging the diffraction surface on the first split surface.

In addition, an objective lens for an optical pickup apparatus iscomposed of plural annular bands split to be in a form of a concentriccircle, and each annular band is corrected in terms of aberration up tothe diffraction limit mostly, for plural light sources each having adifferent wavelength and for transparent substrates each having adifferent thickness of a recording surface, thus, flare light enteringan optical detector is reduced, and manufacturing of the objective lensis easy. “Disclosed embodiment can be varied by a skilled person withoutdeparting from the spirit and scope of the invention”

1. An optical pickup apparatus for recording and/or reproducinginformation for a first, second and third optical disk provided with atransparent substrate, comprising: a first light source configured toemit a first light flux having a first wavelength for recording and/orreproducing information for a second optical disk which is a highdensity optical disk used with a blue laser beam; a second light sourceconfigured to emit a second light flux having a second wavelength longerthan the first wavelength, for recording and/or reproducing informationfor a first optical disk; a third light source configured to emit athird light flux having a third wavelength longer than the secondwavelength, for recording and/or reproducing a third optical disk; andan objective lens having an aspherical refractive surface and aring-shaped diffractive surface designed with a phase differencefunction such that spherical aberrations of the first, second and thirdlight fluxes due to difference in thickness of the transparent substrateamong the first, second and third optical disks are corrected.
 2. Theoptical pickup apparatus of claim 1, wherein when NA2 is an image sidenumerical aperture of the objective lens necessary for recording and/orreproducing information for the first optical disk, NA1 is an image sidenumerical aperture of the objective lens necessary for recording and/orreproducing information for the second optical disk, and NA3 is an imageside numerical aperture of the objective lens necessary for recordingand/or reproducing information for the third optical disk, NA1 and NA2are larger than NA3.
 3. The optical pickup apparatus of claim 2, whereinNA1 is equal to NA2.
 4. The optical pickup apparatus of claim 2, whereinwhen recording and/or reproducing information is conducted for the thirdoptical disk, a spherical aberration of a light flux having passedthrough a region of the objective lens having a numerical aperturelarger than NA3 is flare on the third optical disk.
 5. The opticalpickup apparatus of claim 1, wherein the ring-shaped diffractive surfaceis designed by a phase difference function in which a coefficient of thesecond power term is not zero and a coefficient of a term other than thesecond power term is not zero.
 6. The optical pickup apparatus of claim1, wherein the ring-shaped diffractive surface is designed by a phasedifference function in which a term having a power larger than fourthpower in power series has a coefficient other than zero.
 7. The opticalpickup apparatus of claim 1, wherein the thickness of the transparentsubstrate of the first optical disk is equal to that of the secondoptical disk.
 8. The optical pickup apparatus of claim 1, wherein theobjective lens corrects spherical aberrations due to difference inwavelength among the first, second and third light fluxes.
 9. Theoptical pickup apparatus of claim 1, wherein the objective lens is asingle lens.
 10. The optical pickup apparatus of claim 1, wherein thehigh density optical disk is a next-generation high density opticaldisk.
 11. The optical pickup apparatus of claim 1, wherein the firstoptical disk is a DVD and the third optical disk is a CD.